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Joh F Atkins - One of the best experts on this subject based on the ideXlab platform.
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evidence of efficient Stop Codon readthrough in four mammalian genes
Nucleic Acids Research, 2014Co-Authors: Gary Loughra, Joh F Atkins, Mingyua Chou, Ivaylo Ivanov, Irwi Jungreis, Manolis Kellis, Anmol M Kira, Pavel V AranovAbstract:Stop Codon readthrough is used extensively by viruses to expand their gene expression. Until recent discoveries in Drosophila, only a very limited number of readthrough cases in chromosomal genes had been reported. Analysis of conserved protein coding signatures that extend beyond annotated Stop Codons identified potential Stop Codon readthrough of four mammalian genes. Here we use a modified targeted bioinformatic approach to identify a further three mammalian readthrough candidates. All seven genes were tested experimentally using reporter constructs transfected into HEK-293T cells. Four displayed efficient Stop Codon readthrough, and these have UGA immediately followed by CUAG. Comparative genomic analysis revealed that in the four readthrough candidates containing UGA-CUAG, this motif is conserved not only in mammals but throughout vertebrates with the first six of the seven nucleotides being universally conserved. The importance of the CUAG motif was confirmed using a systematic mutagenesis approach. One gene, OPRL1, encoding an opiate receptor, displayed extremely efficient levels of readthrough (∼31%) in HEK-293T cells. Signals both 5 � and 3 � of the OPRL1 Stop
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cryptic mhc class i binding peptides are revealed by aminoglycoside induced Stop Codon read through into the 3 utr
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Ellio Goodenough, Michael T Howard, Joh F Atkins, Kevi M Flaniga, Tara M Robinso, Matthew Zook, Laurence C EisenlohAbstract:Aminoglycosides have been proposed as therapies for genetic disorders caused by nonsense mutations, because of their capacity to enhance translational read-through of premature termination Codons (PTCs), thereby permitting expression of functional full-length protein. However, a potential consequence of this strategy is the development of an autoimmune response to HLA-presented epitopes encoded downstream of the PTC or other Stop Codons. Using a recombinant virus-expression system in tissue culture and in mice, we demonstrate that gentamicin can induce expression and MHC class I presentation of a model epitope encoded downstream of a PTC at levels sufficient to activate CD8(+) T cells. The degree of read-through-derived peptide presentation varies with the sequence of the Stop Codon and +1 nucleotide. Additionally, we applied a mass spectrometry exploration of the HLA class I peptide repertoire of gentamicin-treated cells and identified multiple peptides derived from read-through of conventional Stop Codons. These results substantiate the possibility of self-reactivity to cryptic epitopes revealed by Stop Codon read-through therapies and potentially other therapeutic approaches involving compounds that alter translational fidelity.
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stimulation of Stop Codon readthrough frequent presence of an extended 3 rna structural element
Nucleic Acids Research, 2011Co-Authors: Andrew E Firth, Raymond F Gesteland, Norma M Wills, Joh F AtkinsAbstract:In Sindbis, Venezuelan equine encephalitis and related alphaviruses, the polymerase is translated as a fusion with other non-structural proteins via readthrough of a UGA Stop Codon. Surprisingly, earlier work reported that the signal for efficient readthrough comprises a single cytidine residue 3'-adjacent to the UGA. However, analysis of variability at synonymous sites revealed strikingly enhanced conservation within the ∼ 150 nt 3'-adjacent to the UGA, and RNA folding algorithms revealed the potential for a phylogenetically conserved stem-loop structure in the same region. Mutational analysis of the predicted structure demonstrated that the stem-loop increases readthrough by up to 10-fold. The same computational analysis indicated that similar RNA structures are likely to be relevant to readthrough in certain plant virus genera, notably Furovirus, Pomovirus, Tobravirus, Pecluvirus and Benyvirus, as well as the Drosophilia gene kelch. These results suggest that 3' RNA stimulatory structures feature in a much larger proportion of readthrough cases than previously anticipated, and provide a new criterion for assessing the large number of cellular readthrough candidates that are currently being revealed by comparative sequence analysis.
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readthrough of dystrophin Stop Codon mutations induced by aminoglycosides
Annals of Neurology, 2004Co-Authors: Michael T Howard, Christine Anderso, Uwe Fass, Shikha Khatri, Raymond F Gesteland, Joh F Atkins, Kevi M FlanigaAbstract:We report the translational readthrough levels induced by the aminoglycosides gentamicin, amikacin, tobramycin, and paromomycin for eight premature Stop Codon mutations identified in Duchenne's and Becker's muscular dystrophy patients. In a transient transfection reporter assay, aminoglycoside treatment results show that one Stop Codon mutation is suppressed significantly better (up to 10% Stop Codon readthrough) than the others; five show lower but statistically significant suppression (<2% Stop Codon readthrough); and two appear refractory to aminoglycoside treatment. Readthrough levels do not substantially vary between different sources of gentamicin, and, for this set of mutations, the efficiency of termination at the premature Stop Codon mutation does not appear to correlate with disease severity.
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sequence specificity of aminoglycoside induced Stop Codon readthrough potential implications for treatment of duchenne muscular dystrophy
Annals of Neurology, 2000Co-Authors: Michael T Howard, Raymond F Gesteland, Kevi M Flaniga, Ia H Shirts, Lori M Petros, Joh F AtkinsAbstract:As a result of their ability to induce translational readthrough of Stop Codons, the aminoglycoside antibiotics are currently being tested for efficacy in the treatment of Duchenne muscular dystrophy patients carrying a nonsense mutation in the dystrophin gene. We have undertaken a systematic analysis of aminoglycoside-induced readthrough of each Stop Codon in human tissue culture cells using a dual luciferase reporter system. Significant differences in the efficiency of aminoglycoside-induced readthrough were observed, with UGA showing greater translational readthrough than UAG or UAA. Additionally, the nucleotide in the position immediately downstream from the Stop Codon had a significant impact on the efficiency of aminoglycoside-induced readthrough in the order C > U > A ≥ G. Our studies show that the efficiency of Stop Codon readthrough in the presence of aminoglycosides is inversely proportional to the efficiency of translational termination in the absence of these compounds. Using the same assay, we analyzed a 33–base pair fragment of the mouse dystrophin gene containing the mdx premature Stop Codon mutation UAA (A), which is also the most efficient translational terminator. The additional flanking sequences from the dystrophin gene do not significantly change the relatively low-level aminoglycoside-induced Stop Codon readthrough of this Stop Codon. The implications of these results for drug efficacy in the treatment of individual patients with Duchenne muscular dystrophy or other genetic diseases caused by nonsense mutations are discussed. Ann Neurol 2000;48:164–169
Jeanpierre Rousse - One of the best experts on this subject based on the ideXlab platform.
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identification of Stop Codon readthrough genes in saccharomyces cerevisiae
Nucleic Acids Research, 2003Co-Authors: Olivie Namy, Guillemette Duchateaunguye, Isabelle Hati, Sylvie Hermannle Denma, Michel Termie, Jeanpierre RousseAbstract:We specifically sought genes within the yeast genome controlled by a non-conventional translation mechanism involving the Stop Codon. For this reason, we designed a computer program using the yeast database genomic regions, and seeking two adjacent open reading frames separated only by a unique Stop Codon (called SORFs). Among the 58 SORFs identified, eight displayed a Stop Codon bypass level ranging from 3 to 25%. For each of the eight sequences, we demonstrated the presence of a poly(A) mRNA. Using isogenic [PSI(+)] and [psi(-)] yeast strains, we showed that for two of the sequences the mechanism used is a bona fide readthrough. However, the six remaining sequences were not sensitive to the PSI state, indicating either a translation termination process independent of eRF3 or a new Stop Codon bypass mechanism. Our results demonstrate that the presence of a Stop Codon in a large ORF may not always correspond to a sequencing error, or a pseudogene, but can be a recoding signal in a functional gene. This emphasizes that genome annotation should take into account the fact that recoding signals could be more frequently used than previously expected.
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translational readthrough of the pde2 Stop Codon modulates camp levels in saccharomyces cerevisiae
Molecular Microbiology, 2002Co-Authors: Olivie Namy, Guillemette Duchateaunguye, Jeanpierre RousseAbstract:Summary The efficiency of translation termination in yeast can vary several 100-fold, depending on the context around the Stop Codon. We performed a computer analysis designed to identify yeast open reading frames (ORFs) containing a readthrough motif surrounding the termination Codon. Eight ORFs were found to display inefficient Stop Codon recognition, one of which, PDE2, encodes the high-affinity cAMP phosphodiesterase. We demonstrate that Pde2p stability is very impaired by the readthrough-dependent extension of the protein. A 20-fold increase in readthrough of PDE2 was observed in a [PSI+] as compared with a [psi–] strain. Consistent with this observation, an important increase in cAMP concentration was observed in suppressor backgrounds. These results provide a molecular explanation for at least some of the secondary phenotypes associated with suppressor backgrounds.
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impact of the six nucleotides downstream of the Stop Codon on translation termination
EMBO Reports, 2001Co-Authors: Olivie Namy, Isabelle Hati, Jeanpierre RousseAbstract:The efficiency of translation termination is influenced by local contexts surrounding Stop Codons. In Saccharomyces cerevisiae, upstream and downstream sequences act synergistically to influence the translation termination efficiency. By analysing derivatives of a leaky Stop Codon context, we initially demonstrated that at least six nucleotides after the Stop Codon are a key determinant of readthrough efficiency in S. cerevisiae. We then developed a combinatorial-based strategy to identify poor 3′ termination contexts. By screening a degenerate oligonucleotide library, we identified a consensus sequence –CA(A/ G)N(U/C/G)A–, which promotes >5% readthrough efficiency when located downstream of a UAG Stop Codon. Potential base pairing between this stimulatory motif and regions close to helix 18 and 44 of the 18S rRNA provides a model for the effect of the 3′ Stop Codon context on translation termination.
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uag readthrough in mammalian cells effect of upstream and downstream Stop Codon contexts reveal different signals
BMC Molecular Biology, 2001Co-Authors: Michel Cassa, Jeanpierre RousseAbstract:Background Translation termination is mediated through an interaction between the release factors eRF1 and eRF3 and the Stop Codon within its nucleotide context. Although it is well known that the nucleotide contexts both upstream and downstream of the Stop Codon, can modulate readthrough, little is known about the mechanisms involved.
Olivie Namy - One of the best experts on this subject based on the ideXlab platform.
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identification of Stop Codon readthrough genes in saccharomyces cerevisiae
Nucleic Acids Research, 2003Co-Authors: Olivie Namy, Guillemette Duchateaunguye, Isabelle Hati, Sylvie Hermannle Denma, Michel Termie, Jeanpierre RousseAbstract:We specifically sought genes within the yeast genome controlled by a non-conventional translation mechanism involving the Stop Codon. For this reason, we designed a computer program using the yeast database genomic regions, and seeking two adjacent open reading frames separated only by a unique Stop Codon (called SORFs). Among the 58 SORFs identified, eight displayed a Stop Codon bypass level ranging from 3 to 25%. For each of the eight sequences, we demonstrated the presence of a poly(A) mRNA. Using isogenic [PSI(+)] and [psi(-)] yeast strains, we showed that for two of the sequences the mechanism used is a bona fide readthrough. However, the six remaining sequences were not sensitive to the PSI state, indicating either a translation termination process independent of eRF3 or a new Stop Codon bypass mechanism. Our results demonstrate that the presence of a Stop Codon in a large ORF may not always correspond to a sequencing error, or a pseudogene, but can be a recoding signal in a functional gene. This emphasizes that genome annotation should take into account the fact that recoding signals could be more frequently used than previously expected.
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translational readthrough of the pde2 Stop Codon modulates camp levels in saccharomyces cerevisiae
Molecular Microbiology, 2002Co-Authors: Olivie Namy, Guillemette Duchateaunguye, Jeanpierre RousseAbstract:Summary The efficiency of translation termination in yeast can vary several 100-fold, depending on the context around the Stop Codon. We performed a computer analysis designed to identify yeast open reading frames (ORFs) containing a readthrough motif surrounding the termination Codon. Eight ORFs were found to display inefficient Stop Codon recognition, one of which, PDE2, encodes the high-affinity cAMP phosphodiesterase. We demonstrate that Pde2p stability is very impaired by the readthrough-dependent extension of the protein. A 20-fold increase in readthrough of PDE2 was observed in a [PSI+] as compared with a [psi–] strain. Consistent with this observation, an important increase in cAMP concentration was observed in suppressor backgrounds. These results provide a molecular explanation for at least some of the secondary phenotypes associated with suppressor backgrounds.
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impact of the six nucleotides downstream of the Stop Codon on translation termination
EMBO Reports, 2001Co-Authors: Olivie Namy, Isabelle Hati, Jeanpierre RousseAbstract:The efficiency of translation termination is influenced by local contexts surrounding Stop Codons. In Saccharomyces cerevisiae, upstream and downstream sequences act synergistically to influence the translation termination efficiency. By analysing derivatives of a leaky Stop Codon context, we initially demonstrated that at least six nucleotides after the Stop Codon are a key determinant of readthrough efficiency in S. cerevisiae. We then developed a combinatorial-based strategy to identify poor 3′ termination contexts. By screening a degenerate oligonucleotide library, we identified a consensus sequence –CA(A/ G)N(U/C/G)A–, which promotes >5% readthrough efficiency when located downstream of a UAG Stop Codon. Potential base pairing between this stimulatory motif and regions close to helix 18 and 44 of the 18S rRNA provides a model for the effect of the 3′ Stop Codon context on translation termination.
Manolis Kellis - One of the best experts on this subject based on the ideXlab platform.
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Stop Codon readthrough generates a c terminally extended variant of the human vitamin d receptor with reduced calcitriol response
Journal of Biological Chemistry, 2018Co-Authors: Gary Loughran, Ivaylo Ivanov, Irwi Jungreis, Manolis Kellis, Ioanna Tzani, Michael Power, Ruslan I Dmitriev, John F AtkinsAbstract:: Although Stop Codon readthrough is used extensively by viruses to expand their gene expression, verified instances of mammalian readthrough have only recently been uncovered by systems biology and comparative genomics approaches. Previously, our analysis of conserved protein coding signatures that extend beyond annotated Stop Codons predicted Stop Codon readthrough of several mammalian genes, all of which have been validated experimentally. Four mRNAs display highly efficient Stop Codon readthrough, and these mRNAs have a UGA Stop Codon immediately followed by CUAG (UGA_CUAG) that is conserved throughout vertebrates. Extending on the identification of this readthrough motif, we here investigated Stop Codon readthrough, using tissue culture reporter assays, for all previously untested human genes containing UGA_CUAG. The readthrough efficiency of the annotated Stop Codon for the sequence encoding vitamin D receptor (VDR) was 6.7%. It was the highest of those tested but all showed notable levels of readthrough. The VDR is a member of the nuclear receptor superfamily of ligand-inducible transcription factors, and it binds its major ligand, calcitriol, via its C-terminal ligand-binding domain. Readthrough of the annotated VDR mRNA results in a 67 amino acid-long C-terminal extension that generates a VDR proteoform named VDRx. VDRx may form homodimers and heterodimers with VDR but, compared with VDR, VDRx displayed a reduced transcriptional response to calcitriol even in the presence of its partner retinoid X receptor.
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evolutionary dynamics of abundant Stop Codon readthrough
Molecular Biology and Evolution, 2016Co-Authors: Irwi Jungreis, Manolis Kellis, Clara S Cha, Robe M Waterhouse, Gabriel FieldsAbstract:Translational Stop Codon readthrough emerged as a major regulatory mechanism affecting hundreds of genes in animal genomes, based on recent comparative genomics and ribosomal profiling evidence, but its evolutionary properties remain unknown. Here, we leverage comparative genomic evidence across 21 Anopheles mosquitoes to systematically annotate readthrough genes in the malaria vector Anopheles gambiae, and to provide the first study of abundant readthrough evolution, by comparison with 20 Drosophila species. Using improved comparative genomics methods for detecting readthrough, we identify evolutionary signatures of conserved, functional readthrough of 353 Stop Codons in the malaria vector, Anopheles gambiae, and of 51 additional Drosophila melanogaster Stop Codons, including several cases of double and triple readthrough and of readthrough of two adjacent Stop Codons. We find that most differences between the readthrough repertoires of the two species arose from readthrough gain or loss in existing genes, rather than birth of new genes or gene death; that readthrough-associated RNA structures are sometimes gained or lost while readthrough persists; that readthrough is more likely to be lost at TAA and TAG Stop Codons; and that readthrough is under continued purifying evolutionary selection in mosquito, based on population genetic evidence. We also determine readthrough-associated gene properties that predate readthrough, and identify differences in the characteristic properties of readthrough genes between clades. We estimate more than 600 functional readthrough Stop Codons in mosquito and 900 in fruit fly, provide evidence of readthrough control of peroxisomal targeting, and refine the phylogenetic extent of abundant readthrough as following divergence from centipede.
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evolutionary dynamics of abundant Stop Codon readthrough in anopheles and drosophila
bioRxiv, 2016Co-Authors: Irwi Jungreis, Robe M Waterhouse, Clara S Cha, Gabriel Fields, Manolis KellisAbstract:Translational Stop Codon readthrough was virtually unknown in eukaryotic genomes until recent developments in comparative genomics and new experimental techniques revealed evidence of readthrough in hundreds of fly genes and several human, worm, and yeast genes. Here, we use the genomes of 21 species of Anopheles mosquitoes and improved comparative techniques to identify evolutionary signatures of conserved, functional readthrough of 353 Stop Codons in the malaria vector, Anopheles gambiae, and 51 additional Drosophila melanogaster Stop Codons, with several cases of double and triple readthrough including readthrough of two adjacent Stop Codons, supporting our earlier prediction of abundant readthrough in pancrustacea genomes. Comparisons between Anopheles and Drosophila allow us to transcend the static picture provided by single-clade analysis to explore the evolutionary dynamics of abundant readthrough. We find that most differences between the readthrough repertoires of the two species are due to readthrough gain or loss in existing genes, rather than to birth of new genes or to gene death; that RNA structures are sometimes gained or lost while readthrough persists; and that readthrough is more likely to be lost at TAA and TAG Stop Codons. We also determine which characteristic properties of readthrough predate readthrough and which are clade-specific. We estimate that there are more than 600 functional readthrough Stop Codons in A. gambiae and 900 in D. melanogaster. We find evidence that readthrough is used to regulate peroxisomal targeting in two genes. Finally, we use the sequenced centipede genome to refine the phylogenetic extent of abundant readthrough.
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evidence of efficient Stop Codon readthrough in four mammalian genes
Nucleic Acids Research, 2014Co-Authors: Gary Loughra, Joh F Atkins, Mingyua Chou, Ivaylo Ivanov, Irwi Jungreis, Manolis Kellis, Anmol M Kira, Pavel V AranovAbstract:Stop Codon readthrough is used extensively by viruses to expand their gene expression. Until recent discoveries in Drosophila, only a very limited number of readthrough cases in chromosomal genes had been reported. Analysis of conserved protein coding signatures that extend beyond annotated Stop Codons identified potential Stop Codon readthrough of four mammalian genes. Here we use a modified targeted bioinformatic approach to identify a further three mammalian readthrough candidates. All seven genes were tested experimentally using reporter constructs transfected into HEK-293T cells. Four displayed efficient Stop Codon readthrough, and these have UGA immediately followed by CUAG. Comparative genomic analysis revealed that in the four readthrough candidates containing UGA-CUAG, this motif is conserved not only in mammals but throughout vertebrates with the first six of the seven nucleotides being universally conserved. The importance of the CUAG motif was confirmed using a systematic mutagenesis approach. One gene, OPRL1, encoding an opiate receptor, displayed extremely efficient levels of readthrough (∼31%) in HEK-293T cells. Signals both 5 � and 3 � of the OPRL1 Stop
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evidence of abundant Stop Codon readthrough in drosophila and other metazoa
Genome Research, 2011Co-Authors: Irwi Jungreis, Rebecca Spokony, Clara S Cha, Nicolas Negre, Alec Victorse, Kevi P White, Manolis KellisAbstract:.While translational Stop Codon readthrough is often used by viral genomes, it has been observed for only a handful of eukaryotic genes. We previously used comparative genomics evidence to recognize protein-coding regions in 12 species of Drosophila and showed that for 149 genes, the open reading frame following the Stop Codon has a protein-coding conservationsignature,hintingthatStopCodonreadthroughmightbecommoninDrosophila.Wereturntothisobservationarmed with deep RNA sequence data from the modENCODE project, an improved higher-resolution comparative genomics metric for detecting protein-coding regions, comparative sequence information from additional species, and directed experimental evidence. We report an expanded set of 283 readthrough candidates, including 16 double-readthrough candidates; these were manually curated to rule out alternatives such as A-to-I editing, alternative splicing, dicistronic translation, and selenocysteine incorporation. We report experimental evidence of translation using GFP tagging and mass spectrometry for several readthrough regions. We find that the set of readthrough candidates differs from other genes in length, composition, conservation, Stop Codon context, and in some cases, conserved stem–loops, providing clues about readthrough regulation and potential mechanisms. Lastly, we expand our studies beyond Drosophila and find evidence of abundant readthrough in several other insect species and one crustacean, and several readthrough candidates in nematode andhuman,suggestingthatfunctionallyimportanttranslational StopCodonreadthroughissignificantlymoreprevalentin Metazoa than previously recognized. [Supplemental material is available for this article.]
Warren P. Tate - One of the best experts on this subject based on the ideXlab platform.
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decoding the translational termination signal the polypeptide chain release factor in escherichia coli crosslinks to the base following the Stop Codon
RNA, 1997Co-Authors: Elizabeth S Poole, Richard Brimacombe, Warren P. TateAbstract:Protein release factors act like tRNA analogues in decoding translational Stop signals. Statistical analysis of the sequences at translational Stop sites and functional studies with particular signals indicate this mimicry involves an increase in the length of the signal in the mRNA. The base following the Stop Codon (+4 base) is of particular interest because it has a strong influence on the competitiveness of the Stop signal at recoding sites, suggesting it might form part of the release factor recognition element. Site-directed crosslinking from the +4 base showed that it is in close proximity to the Escherichia coli release factor-2 in a termination complex, a prerequisite for the +4 base being part of the recognition element. Fingerprinting analysis indicates that crosslinking to the release factor occurred from both +1 and +4 positions of the Stop signal in the same RNA molecule. This provides more evidence that the +4 base may be an integral part of the decoding signature in the mRNA during the termination phase of protein biosynthesis.
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translational termination efficiency in mammals is influenced by the base following the Stop Codon
Proceedings of the National Academy of Sciences of the United States of America, 1995Co-Authors: Kim K Mccaugha, Mark E Dalphi, Marla J Erry, Warren P. TateAbstract:The base following Stop Codons in mammalian genes is strongly biased, suggesting that it might be important for the termination event. This proposal has been tested experimentally both in vivo by using the human type I iodothyronine deiodinase mRNA and the recoding event at the internal UGA Codon and in vitro by measuring the ability of each of the 12 possible 4-base Stop signals to direct the eukaryotic polypeptide release factor to release a model peptide, formylmethionine, from the ribosome. The internal UGA in the deiodinase mRNA is used as a Codon for incorporation of selenocysteine into the protein. Changing the base following this UGA Codon affected the ratio of termination to selenocysteine incorporation in vivo at this Codon: 1:3 (C or U) and 3:1 (A or G). These UGAN sequences have the same order of efficiency of termination as was found with the in vitro termination assay (4th base: A approximately G >> C approximately U). The efficiency of in vitro termination varied in the same manner over a 70-fold range for the UAAN series and over an 8-fold range for the UGAN and UAGN series. There is a correlation between the strength of the signals and how frequently they occur at natural termination sites. Together these data suggest that the base following the Stop Codon influences translational termination efficiency as part of a larger termination signal in the expression of mammalian genes.
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the identity of the base following the Stop Codon determines the efficiency of in vivo translational termination in escherichia coli
The EMBO Journal, 1995Co-Authors: Elizabeth S Poole, Warren P. TateAbstract:A statistical analysis of > 2000 Escherichia coli genes suggested that the base following the translational Stop Codon might be an important feature of the signal for termination. The strengths of each of 12 possible 'four base Stop signals' (UAAN, UGAN and UAGN) were tested in an in vivo termination assay that measured termination efficiency by its direct competition with frameshifting. Termination efficiencies varied significantly depending on both the Stop Codon and the fourth base, ranging from 80 (UAAU) to 7% (UGAC). For both the UAAN and UGAN series, the fourth base hierarchy was U > G > A approximately C. UAG Stop Codons, which are used rarely in E. coli, showed efficiencies comparable with UAAN and UGAN, but differed in that the hierarchy of the fourth base was G > U approximately A > C. The rate of release factor selection varied 30-fold at UGAN Stop signals, and 10-fold for both the UAAN and UAGN series; it correlated well with the frequency with which the different UAAN and UGAN signals are found at natural termination sites. The results suggest that the identity of the base following the Stop Codon determines the efficiency of translational termination in E. coli. They also provide a rationale for the use of the strong UAAU signal in highly expressed genes and for the occurrence of the weaker UGAC signal at several recording sites.
