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Marita Cohn - One of the best experts on this subject based on the ideXlab platform.
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Single- and double-stranded DNA binding Proteins act in concert to conserve a telomeric DNA core sequence
Genome Integrity, 2011Co-Authors: Jenny Rhodin Edsö, Cecilia Gustafsson, Marita CohnAbstract:Background Telomeres are protective cap structures at the ends of the linear eukaryotic chromosomes, which provide stability to the genome by shielding from degradation and chromosome fusions. The cap consists of telomere-specific Proteins binding to the respective single- and double-stranded parts of the telomeric sequence. In addition to the nucleation of the chromatin structure the telomere-binding Proteins are involved in the regulation of the telomere length. However, the telomeric sequences are highly diverged among yeast species. During the evolution this high rate of divergency presents a challenge for the sequence recognition of the telomere-binding Proteins. Results We found that the Saccharomyces castellii Protein Rap1, a negative regulator of telomere length, binds a 12-mer minimal binding site (MBS) within the double-stranded telomeric DNA. The sequence specificity is dependent on the interaction with two 5 nucleotide motifs, having a 6 nucleotide centre-to-centre spacing. The isolated DNA-binding domain binds the same MBS and retains the same motif binding characteristics as the full-length Rap1 Protein. However, it shows some deviations in the degree of sequence-specific dependence in some nucleotide positions. Intriguingly, the positions of most importance for the sequence-specific binding of the full-length Rap1 Protein coincide with 3 of the 4 nucleotides utilized by the 3' overhang binding Protein Cdc13. These nucleotides are very well conserved within the otherwise highly divergent telomeric sequences of yeasts. Conclusions Rap1 and Cdc13 are two very distinct types of DNA-binding Proteins with highly separate functions. They interact with the double-stranded vs. the single-stranded telomeric DNA via significantly different types of DNA-binding domain structures. However, we show that they are dependent on coinciding nucleotide positions for their sequence-specific binding to telomeric sequences. Thus, we conclude that during the molecular evolution they act together to preserve a core sequence of the telomeric DNA.
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Single- and double-stranded DNA binding Proteins act in concert to conserve a telomeric DNA core sequence
Genome integrity, 2011Co-Authors: Jenny Rhodin Edsö, Cecilia Gustafsson, Marita CohnAbstract:Telomeres are protective cap structures at the ends of the linear eukaryotic chromosomes, which provide stability to the genome by shielding from degradation and chromosome fusions. The cap consists of telomere-specific Proteins binding to the respective single- and double-stranded parts of the telomeric sequence. In addition to the nucleation of the chromatin structure the telomere-binding Proteins are involved in the regulation of the telomere length. However, the telomeric sequences are highly diverged among yeast species. During the evolution this high rate of divergency presents a challenge for the sequence recognition of the telomere-binding Proteins. We found that the Saccharomyces castellii Protein Rap1, a negative regulator of telomere length, binds a 12-mer minimal binding site (MBS) within the double-stranded telomeric DNA. The sequence specificity is dependent on the interaction with two 5 nucleotide motifs, having a 6 nucleotide centre-to-centre spacing. The isolated DNA-binding domain binds the same MBS and retains the same motif binding characteristics as the full-length Rap1 Protein. However, it shows some deviations in the degree of sequence-specific dependence in some nucleotide positions. Intriguingly, the positions of most importance for the sequence-specific binding of the full-length Rap1 Protein coincide with 3 of the 4 nucleotides utilized by the 3' overhang binding Protein Cdc13. These nucleotides are very well conserved within the otherwise highly divergent telomeric sequences of yeasts. Rap1 and Cdc13 are two very distinct types of DNA-binding Proteins with highly separate functions. They interact with the double-stranded vs. the single-stranded telomeric DNA via significantly different types of DNA-binding domain structures. However, we show that they are dependent on coinciding nucleotide positions for their sequence-specific binding to telomeric sequences. Thus, we conclude that during the molecular evolution they act together to preserve a core sequence of the telomeric DNA.
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DNA binding and telomere length regulation of yeast Rap1 homologues.
Journal of molecular biology, 2003Co-Authors: Johan Wahlin, Monika Rosén, Marita CohnAbstract:Abstract The repressor activator Protein 1 ( Rap1 ) has many important functions in Saccharomyces cerevisiae . At the chromosome ends, it is a negative regulator of telomere length. Here, we show that Saccharomyces castellii / Saccharomyces dairensis telomeric sequences inserted into a S. cerevisiae telomere are counted as part of the telomere, consistent with the presence of high-affinity Rap1p binding sites within these sequences. We show that S. castellii Rap1p (scasRap1p) can regulate telomere length in a S. cerevisiae strain, albeit less stringently. Cloning of the S. dairensis Rap1 homologue ( sdaiRap1 ) revealed that it encodes the largest Rap1 Protein identified to date. Despite its large size, binding analyses of the recombinant sdaiRap1p revealed that the Protein binds with the same spacing and with similar affinity to yeast telomeric sequences, as the scer - and scasRap1 Proteins. According to the Rap1p counting model for telomere length regulation, a low density of Rap1p binding sites in a telomere would result in a longer telomere in S. cerevisiae . We have compared the lengths of two individual S. dairensis telomeres and find that their lengths are not regulated to give the same number of high-affinity binding sites. This may be due to other factors than Rap1p having influence on the telomere length regulation.
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Analysis of the Rap1 Protein binding to homogeneous telomeric repeats in Saccharomyces castellii.
Yeast (Chichester England), 2002Co-Authors: Johan Wahlin, Marita CohnAbstract:The repressor activator Protein 1 (Rap1) plays a role in telomere structure and function inS. cerevisiae. Here, the Rap1 homologue was identified and cloned from the budding yeast Saccharomyces castellii (scasRap1). The scasRap1 gene encodes a Protein of 826 amino acids and shares an overall high degree of similarity with the S. cerevisiae Rap1 (scerRap1). We demonstrate that the scasRap1 is able to complement scerRap1 in temperature-sensitive S. cerevisiae strains and is able to function as a regulator to maintain the original telomere lengths. Binding analyses of the E. coli-expressed scasRap1 Protein demonstrate that it needs two consecutive telomeric repeats in order to bind the S. castellii telomeric DNA sequences, and that it binds adjacent sites having a 16 bp centre-to-centre spacing. The binding affinity to telomeric DNA of several other yeasts is similar to that of scerRap1p. However, in contrast to scerRap1p, scasRap1p was found to bind the human telomeric sequence. Moreover, the scasRap1p was found to incorporate a variant repeat in its binding to the otherwise homogeneous telomeric DNA of S. castellii. This ability to bind various sites differing in DNA sequence indicates a high degree of adjustability in the binding of scasRap1p to DNA.
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Saccharomyces cerevisiae Rap1 binds to telomeric sequences with spatial flexibility
Nucleic acids research, 2000Co-Authors: Johan Wahlin, Marita CohnAbstract:A wide divergence has been detected in the telomeric sequences among budding yeast species. Despite their length and homogeneity differences, all these yeast telomeric sequences show a conserved core which closely matches the consensus Rap1-binding sequence. We demonstrate that the Rap1 Protein binds this sequence core, without involving the diverged sequences outside the core. In Saccharomyces castellii and Saccharomyces dairensis specific classes of interspersed variant repeats are present. We show here that a Rap1-binding site is formed in these species by connecting two consecutive 8 bp telomeric repeats. DNase I footprint analyses specify the binding site as the 13 bp sequence CTGGGTGTCTGGG. The Rap1 Protein also binds the variant repeats, although with a lowered affinity. However, a split footprint is produced when Rap1 binds a variant repeat where the two half-sites of the binding site are separated by an additional 6 nt. This is probably caused by the intervening sequence looping out of the Rap1–DNA complex. We suggest that the bipartite subdomain structure of the Rap1 Protein allows it to remodel telomeric chromatin, a feature which may be of great relevance for telomeric chromatin assembly and structure in vivo.
David Shore - One of the best experts on this subject based on the ideXlab platform.
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In Vivo Topography of Rap1p-DNA Complex at Saccharomyces cerevisiae TEF2 UASRPG During Transcriptional Regulation
Journal of molecular biology, 2002Co-Authors: Veronica De Sanctis, David Shore, Sabrina La Terra, Alessandro Bianchi, Luciano Burderi, Ernesto Di Mauro, Rodolfo NegriAbstract:Abstract We have analyzed in detail the structure of Rap1–UASRPG complexes in Saccharomyces cerevisiae cells using multi-hit KMnO4, UV and micrococcal nuclease high-resolution footprinting. Three copies of the Rap1 Protein are bound to the promoter simultaneously in exponentially growing cells, as shown by KMnO4 multi-hit footprinting analysis, causing extended and diagnostic changes in the DNA structure of the region containing the UASRPG. Amino acid starvation does not cause loss of Rap1p from the complex; however, in vivo UV-footprinting reveals the occurrence of structural modifications of the complex. Moreover, low-resolution micrococcal nuclease digestion shows that the chromatin of the entire region is devoid of positioned nucleosomes but is susceptible to changes in accessibility to the nuclease upon amino acid starvation. The implications of these results for the mechanism of Rap1p action are discussed.
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A novel Rap1p-interacting factor, Rif2p, cooperates with Rif1p to regulate telomere length in Saccharomyces cerevisiae.
Genes & development, 1997Co-Authors: David Wotton, David ShoreAbstract:The Saccharomyces cerevisiae Rap1 Protein binds with high affinity to sites within the poly(C(1-3)A) tracts at telomeres, where it plays a role in both telomere length regulation and the initiation of telomeric silencing. Rap1p initiates silencing at telomeres by interacting through its carboxy-terminal domain with Sir3p and Sir4p, both of which are required for repression. This same domain of Rap1p also negatively regulates telomere elongation, through an unknown mechanism. We have identified a new Rap1-interacting factor (Rif2p) that plays a role in telomere length regulation. Rif2p has considerable functional similarities with a Rap1p-interacting factor (Rif1p) identified previously. Mutations in RIF1 or RIF2 (unlike mutations in the silencing genes SIR3 and SIR4) result in moderate telomere elongation and improved telomeric silencing. However, deletion of both RIF1 and RIF2 in the same cell results in a dramatic increase in telomere length, similar to that seen with a carboxy-terminal truncation of Rap1p. In addition, overexpression of either RIF1 or RIF2 decreases telomere length, and co-overexpression of these Proteins can reverse the telomere elongation effect of overexpression of the Rap1p carboxyl terminus. Finally, we show that Rif1p and Rif2p can interact with each other in vivo. These results suggest that telomere length regulation is mediated by a Protein complex consisting of Rif1p and Rif2p, each of which has distinct regulatory functions. One role of Rap1p in telomere length regulation is to recruit these Proteins to the telomeres.
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evidence that a complex of sir Proteins interacts with the silencer and telomere binding Protein Rap1
Genes & Development, 1994Co-Authors: Paolo Moretti, Katie Freeman, Lavanya Coodly, David ShoreAbstract:The maintenance of transcriptional silencing at HM mating-type loci and telomeres in yeast requires the SIR2, SIR3, and SIR4 Proteins, none of which appear to be DNA-binding Proteins. Here we show that SIR3 and SIR4 interact with a carboxy-terminal domain of the silencer, telomere, and UAS-binding Protein Rap1. We identified SIR3 and SIR4 in a two-hybrid screen for RAPl-interacting factors and showed that SIR3 interacts both with itself and with SIR4. The interaction between Rap1 and SIR3 can be observed in vitro in the absence of other yeast Proteins. Consistent with the notion that native SIR Proteins interact with the Rap1 carboxyl terminus, we show that mutation of the endogenous SIR3 and SIR4 genes increases transcriptional activation by LexA/Rap1 hybrids. To test the importance of the Rap1-SIR3 interaction for silencing, we identified mutations in the Rap1 carboxyl terminus that either diminish or abolish this interaction. When introduced into the native Rap1 Protein, these mutations cause corresponding defects in silencing at both HMR and telomeres. We propose that Rap1 acts in the initiation of transcriptional silencing by recruiting a complex of SIR Proteins to the chromosome via Protein-Protein interactions. These data are consistent with a model in which SIR3 and SIR4 play a structural role in the maintenance of silent chromatin and indicate that their action is initiated at the silencer itself.
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Epigenetic switching of transcriptional states: cis- and trans-acting factors affecting establishment of silencing at the HMR locus in Saccharomyces cerevisiae.
Molecular and cellular biology, 1993Co-Authors: Lori Sussel, David Vannier, David ShoreAbstract:In this study, we used the ADE2 gene in a colony color assay to monitor transcription from the normally silent HMR mating-type locus in Saccharomyces cerevisiae. This sensitive assay reveals that some previously identified cis- and trans-acting mutations destabilize silencing, causing genetically identical cells to switch between repressed and derepressed transcriptional states. Deletion of the autonomously replicating sequence (ARS) consensus element at the HMR-E silencer or mutation of the silencer binding Protein Rap1 (Rap1s) results in the presence of large sectors within individual colonies of both repressed (Ade-, pink) and derepressed (Ade+, white) cells. These results suggest that both the ARS consensus element and the Rap1 Protein play a role in the establishment of repression at HMR. In diploid cells, the two copies of HMR appear to behave identically, suggesting that the switching event, though apparently stochastic, reflects some property of the cell rather than a specific event at each HMR locus. In the ADE2 assay system, silencing depends completely upon the function of the SIR genes, known trans-acting regulators of the silent loci, and is sensitive to the gene dosage of two SIR genes, SIR1 and SIR4. Using the ADE2 colony color assay in a genetic screen for suppressors of Rap1s, silencer ARS element deletion double mutants, we have identified a large number of genes that may affect the establishment of repression at the HMR silent mating-type locus.
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A Rap1-interacting Protein involved in transcriptional silencing and telomere length regulation.
Genes & development, 1992Co-Authors: C. F. J. Hardy, Lori Sussel, David ShoreAbstract:The yeast Rap1 Protein is a sequence-specific DNA-binding Protein that functions as both a repressor and an activator of transcription. Rap1 is also involved in the regulation of telomere structure, where its binding sites are found within the terminal poly(C1-3A) sequences. Previous studies have indicated that the regulatory function of Rap1 is determined by the context of its binding site and, presumably, its interactions with other factors. Using the two-hybrid system, a genetic screen for the identification of Protein-Protein interactions, we have isolated a gene encoding a Rap1-interacting factor (RIF1). Strains carrying gene disruptions of RIF1 grow normally but are defective in transcriptional silencing and telomere length regulation, two phenotypes strikingly similar to those of silencing-defective Rap1s mutants. Furthermore, hybrid Proteins containing Rap1s missense mutations are defective in an interaction with RIF1 in the two-hybrid system. Taken together, these data support the idea that the Rap1s phenotypes are attributable to a failure to recruit RIF1 to silencers and telomeres and suggest that RIF1 is a cofactor or mediator for Rap1 in the establishment of a repressed chromatin state at these loci. By use of the two-hybrid system, we have isolated a mutation in RIF1 that partially restores the interaction with Rap1s mutant Proteins.
Shaomeng Wang - One of the best experts on this subject based on the ideXlab platform.
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design of high affinity stapled peptides to target the repressor activator Protein 1 Rap1 telomeric repeat binding factor 2 trf2 Protein Protein interaction in the shelterin complex
Journal of Medicinal Chemistry, 2016Co-Authors: Xu Ran, Yong Chen, Liu Liu, Chao Yie Yang, Ming Lei, Shaomeng WangAbstract:Shelterin, a six-Protein complex, plays a fundamental role in protecting both the length and the stability of telomeres. Repressor activator Protein 1 (Rap1) and telomeric repeat-binding factor 2 (TRF2) are two subunits in shelterin that interact with each other. Small-molecule inhibitors that block the Rap1/TRF2 Protein–Protein interaction can disrupt the structure of shelterin and may be employed as pharmacological tools to investigate the biology of shelterin. On the basis of the cocrystal structure of Rap1/TRF2 complex, we have developed first-in-class triazole-stapled peptides that block the Protein–Protein interaction between Rap1 and TRF2. Our most potent stapled peptide binds to Rap1 Protein with a Ki value of 7 nM and is >100 times more potent than the corresponding wild-type TRF2 peptide. On the basis of our high-affinity peptides, we have developed and optimized a competitive, fluorescence polarization (FP) assay for accurate and rapid determination of the binding affinities of our designed com...
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Design of High-Affinity Stapled Peptides To Target the Repressor Activator Protein 1 (Rap1)/Telomeric Repeat-Binding Factor 2 (TRF2) Protein–Protein Interaction in the Shelterin Complex
Journal of medicinal chemistry, 2015Co-Authors: Xu Ran, Yong Chen, Liu Liu, Chao Yie Yang, Ming Lei, Shaomeng WangAbstract:Shelterin, a six-Protein complex, plays a fundamental role in protecting both the length and the stability of telomeres. Repressor activator Protein 1 (Rap1) and telomeric repeat-binding factor 2 (TRF2) are two subunits in shelterin that interact with each other. Small-molecule inhibitors that block the Rap1/TRF2 Protein-Protein interaction can disrupt the structure of shelterin and may be employed as pharmacological tools to investigate the biology of shelterin. On the basis of the cocrystal structure of Rap1/TRF2 complex, we have developed first-in-class triazole-stapled peptides that block the Protein-Protein interaction between Rap1 and TRF2. Our most potent stapled peptide binds to Rap1 Protein with a Ki value of 7 nM and is >100 times more potent than the corresponding wild-type TRF2 peptide. On the basis of our high-affinity peptides, we have developed and optimized a competitive, fluorescence polarization (FP) assay for accurate and rapid determination of the binding affinities of our designed compounds and this assay may also assist in the discovery of non-peptide, small-molecule inhibitors capable of blocking the Rap1/TRF2 Protein-Protein interaction.
Johan Wahlin - One of the best experts on this subject based on the ideXlab platform.
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DNA binding and telomere length regulation of yeast Rap1 homologues.
Journal of molecular biology, 2003Co-Authors: Johan Wahlin, Monika Rosén, Marita CohnAbstract:Abstract The repressor activator Protein 1 ( Rap1 ) has many important functions in Saccharomyces cerevisiae . At the chromosome ends, it is a negative regulator of telomere length. Here, we show that Saccharomyces castellii / Saccharomyces dairensis telomeric sequences inserted into a S. cerevisiae telomere are counted as part of the telomere, consistent with the presence of high-affinity Rap1p binding sites within these sequences. We show that S. castellii Rap1p (scasRap1p) can regulate telomere length in a S. cerevisiae strain, albeit less stringently. Cloning of the S. dairensis Rap1 homologue ( sdaiRap1 ) revealed that it encodes the largest Rap1 Protein identified to date. Despite its large size, binding analyses of the recombinant sdaiRap1p revealed that the Protein binds with the same spacing and with similar affinity to yeast telomeric sequences, as the scer - and scasRap1 Proteins. According to the Rap1p counting model for telomere length regulation, a low density of Rap1p binding sites in a telomere would result in a longer telomere in S. cerevisiae . We have compared the lengths of two individual S. dairensis telomeres and find that their lengths are not regulated to give the same number of high-affinity binding sites. This may be due to other factors than Rap1p having influence on the telomere length regulation.
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Analysis of the Rap1 Protein binding to homogeneous telomeric repeats in Saccharomyces castellii.
Yeast (Chichester England), 2002Co-Authors: Johan Wahlin, Marita CohnAbstract:The repressor activator Protein 1 (Rap1) plays a role in telomere structure and function inS. cerevisiae. Here, the Rap1 homologue was identified and cloned from the budding yeast Saccharomyces castellii (scasRap1). The scasRap1 gene encodes a Protein of 826 amino acids and shares an overall high degree of similarity with the S. cerevisiae Rap1 (scerRap1). We demonstrate that the scasRap1 is able to complement scerRap1 in temperature-sensitive S. cerevisiae strains and is able to function as a regulator to maintain the original telomere lengths. Binding analyses of the E. coli-expressed scasRap1 Protein demonstrate that it needs two consecutive telomeric repeats in order to bind the S. castellii telomeric DNA sequences, and that it binds adjacent sites having a 16 bp centre-to-centre spacing. The binding affinity to telomeric DNA of several other yeasts is similar to that of scerRap1p. However, in contrast to scerRap1p, scasRap1p was found to bind the human telomeric sequence. Moreover, the scasRap1p was found to incorporate a variant repeat in its binding to the otherwise homogeneous telomeric DNA of S. castellii. This ability to bind various sites differing in DNA sequence indicates a high degree of adjustability in the binding of scasRap1p to DNA.
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Rap1 at the Yeast Telomere
2002Co-Authors: Johan WahlinAbstract:Telomeres are specialized complexes of DNA and Proteins that cap and confer stability to the ends of eukaryotic chromosomes. The telomeric DNA of most eukaryotes is composed of tandemly arranged short repeats. Within the budding yeasts these repeats are diverged in length as well as in nucleotide composition. However, they contain a sequence resembling the consensus binding sequence of the major telomere-binding Protein Repressor Activator Protein 1 (Rap1p). It is shown here that the telomeric repeat units of several budding yeasts are indeed bound by the Saccharomyces cerevisiae Rap1 Protein(scerRap1p) in vitro. Furthermore, the Protein can bind to some of those sequences with spatial flexibility. The identification of two novel Rap1 homologues are also presented here. They were isolated from Saccharomyces castellii (scasRap1) and Saccharomyces dairensis (sdaiRap1). Sequence analyses revealed that the DNA-binding and C-terminal domains of these Proteins are similar to the corresponding regions of scerRap1p, reflecting the importance of these regions in the function of the Protein. The similarity between the Proteins is underscored by the finding that the scasRap1 gene can replace the scerRap1 gene in a S. cerevisiae strain. Binding analyses revealed that the scas- and sdaiRap1 Proteins bind to telomeric sequences in a similar manner as scerRap1p. However unlike scerRap1p, these Proteins can bind to the telomeric repeats of vertebrates in vitro. It is shown here that telomeric repeats from S. castellii/S. dairensis introduced into a S. cerevisiae telomere are sensed as being part of the telomere by the telomere length sensing mechanism. Such hybrid telomeres are kept at slightly shorter lengths than telomeres containing S. cerevisiae telomeric DNA only. Since these S. castellii/S. dairensis telomeric repeats have a denser distribution of Rap1p binding sites than S. cerevisiae telomeric DNA, this shortening of the telomeric tracts would be predicted from the Rap1 Protein counting model of telomere length regulation.
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Saccharomyces cerevisiae Rap1 binds to telomeric sequences with spatial flexibility
Nucleic acids research, 2000Co-Authors: Johan Wahlin, Marita CohnAbstract:A wide divergence has been detected in the telomeric sequences among budding yeast species. Despite their length and homogeneity differences, all these yeast telomeric sequences show a conserved core which closely matches the consensus Rap1-binding sequence. We demonstrate that the Rap1 Protein binds this sequence core, without involving the diverged sequences outside the core. In Saccharomyces castellii and Saccharomyces dairensis specific classes of interspersed variant repeats are present. We show here that a Rap1-binding site is formed in these species by connecting two consecutive 8 bp telomeric repeats. DNase I footprint analyses specify the binding site as the 13 bp sequence CTGGGTGTCTGGG. The Rap1 Protein also binds the variant repeats, although with a lowered affinity. However, a split footprint is produced when Rap1 binds a variant repeat where the two half-sites of the binding site are separated by an additional 6 nt. This is probably caused by the intervening sequence looping out of the Rap1–DNA complex. We suggest that the bipartite subdomain structure of the Rap1 Protein allows it to remodel telomeric chromatin, a feature which may be of great relevance for telomeric chromatin assembly and structure in vivo.
Elizabeth H. Blackburn - One of the best experts on this subject based on the ideXlab platform.
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Rap1 Protein regulates telomere turnover in yeast
Proceedings of the National Academy of Sciences of the United States of America, 1998Co-Authors: Anat Krauskopf, Elizabeth H. BlackburnAbstract:Telomere length is maintained through a dynamic balance between addition and loss of the terminal telomeric DNA. Normal telomere length regulation requires telomerase as well as a telomeric Protein–DNA complex. Previous work has provided evidence that in the budding yeasts Kluyveromyces lactis and Saccharomyces cerevisiae, the telomeric double-stranded DNA binding Protein Rap1p negatively regulates telomere length, in part by nucleating, by its C-terminal tail, a higher-order DNA binding Protein complex that presumably limits access of telomerase to the chromosome end. Here we show that in K. lactis, truncating the Rap1p C-terminal tail (Rap1p-ΔC mutant) accelerates telomeric repeat turnover in the distal region of the telomere. In addition, combining the Rap1-ΔC mutation with a telomerase template mutation (ter1-kpn), which directs the addition of mutated telomeric DNA repeats to telomeres, synergistically caused an immediate loss of telomere length regulation. Capping of the unregulated telomeres of these double mutants with functionally wild-type repeats restored telomere length control. We propose that the rate of terminal telomere turnover is controlled by Rap1p specifically through its interactions with the most distal telomeric repeats.
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Telomeric sequence diversity within the genus Saccharomyces
Current genetics, 1998Co-Authors: Marita Cohn, Michael J. Mceachern, Elizabeth H. BlackburnAbstract:Conservation of telomeric DNA repeat sequences has been found across evolutionarily diverse eukaryotes. Here we report on a marked telomeric sequence diversity within the budding yeast genus Saccharomyces. Cloning and sequencing of telomeric repeat units from S. castellii, S. dairensis, S. exiguus and S. kluyveri showed a length variation between 8 and 26 bp, as well as a distinct variation in the degree of homogeneity, among the species. In S. castellii and S. dairensis, TCTGGGTG constituted a majority of the telomeric repeat units. However, the character of the variant repeats differed: in S. castellii the major class of variant repeats contained additional TG dinucleotides per repeat unit, [TCTGGGTG(TG)1–3], whereas in S. dairensis the major variant repeat is the shorter, uniform sequence TCTGGG. This result suggests mechanistic differences in the action of the telomerases of these closely related yeasts. Despite their length and homogeneity differences, all the Saccharomyces telomeric sequences show a conserved core which is also shared by the Candida glabrata telomeric sequence. This evolutionary similarity may be partly explained by the preservation of a binding site for the Rap1 Protein.
