The Experts below are selected from a list of 1365 Experts worldwide ranked by ideXlab platform
Alice Telesnitsky - One of the best experts on this subject based on the ideXlab platform.
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Pseudodiploid genome organization AIDS full-length human immunodeficiency virus type 1 DNA synthesis.
Journal of virology, 2007Co-Authors: Steven R. King, Nisha K. Duggal, Clement B. Ndongmo, Crystal Pacut, Alice TelesnitskyAbstract:Template switching between copackaged human immunodeficiency virus type 1 (HIV-1) genomic RNAs is genetically silent when identical RNAs are copackaged but yields recombinants when virions contain two distinct RNAs. Sequencing has revealed that errors at retroviral recombination junctions are infrequent, suggesting that template switching is not intrinsically mutagenic. Here, we tested the hypothesis that template switching may instead contribute to replication fidelity. This hypothesis predicts that reverse transcription of a single-copy gene will be more error prone than replication in the presence of a second copy. To test this, HIV-1-based vectors containing both lacZ and the puromycin resistance marker were expressed either alone or with an excess of an "empty" vector lacking lacZ and puro. This resulted in virions with either RNA homodimers or haploid genomes with only a single lacZ-puro RNA. In untreated cells, lacZ inactivation rates suggested that haploid vector reverse transcription was slightly more error prone than that of homodimerized Pseudodiploid vectors. Haploid reverse transcription was at least threefold more error prone than Pseudodiploid-templated synthesis when slowed by hydroxyurea treatment or stopped prematurely with zidovudine. Individual products of one- and two-copy genes revealed both nucleotide substitutions and deletions, with deletions more frequent than point mutations among haploid genome products. Similar spectra of defective products were observed at early reverse transcription time points and among products of haploid virions. These results indicate that faithful, full-length reverse transcription products were underrepresented in the absence of a reserve of genetic information and suggest that template switching contributes to HIV-1 genomic integrity.
Claude Szpirer - One of the best experts on this subject based on the ideXlab platform.
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The effect of ploidy and colcemid on the frequency of spontaneous transformation of cultured cells
Cell Biology International Reports, 2004Co-Authors: Daniela Saggioro, Josiane Szpirer, Claude SzpirerAbstract:Abstract The frequency of spontaneous transformation, defined as the acquisition of the ability to form colonies in soft agar (anchorage independence) was compared in rat fibroblasts of recently established lines possessing Pseudodiploid to pseudotetraploid numbers of chromosomes. Transformation frequency appeared to be independent on the ploidy level. The effect of colcemid on the transformation frequency of Pseudodiploid fibroblasts was also examined. Colcemid treatment resulted in an increased frequency of transformation. In addition, most of the transformed clones, either derived from colcemid-treated cells, or derived from untreated cells, were characterized by significant changes in chromosome number. These results cannot be easily reconciled with the hypothesis that the main cause of spontaneous transformation is the appearance of recessive mutations. They rather support the idea that this conversion is the consequence of alterations in the number of certain chromosomes.
E L Blewett - One of the best experts on this subject based on the ideXlab platform.
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Construction of herpes simplex viruses that are Pseudodiploid for the glycoprotein B gene: a strategy for studying the function of an essential herpesvirus gene.
The Journal of general virology, 1991Co-Authors: V Misra, E L BlewettAbstract:The primary structure of glycoprotein B (gB) is conserved strongly among many members of the Herpesviridae, including some that differ vastly in their natural properties. To determine whether the structural similarity between the gBs of herpes simplex virus type 1 (HSV-1) and bovine herpesvirus type 1 (BHV-1) was reflected in functional homology, we constructed Pseudodiploid HSV-1 virions which, in addition to their own gene encoding gB, also contained a gene for encoding BHV-1 gB. Two kinds of Pseudodiploid viruses were constructed. In one, the coding sequences of the BHV-1 gB gene were linked to the 5' flanking sequences of the HSV-1 thymidine kinase (TK) gene. In the other, the entire BHV-1 gB gene, including its own flanking sequences, was introduced into the TK gene. In cells infected with the viruses both HSV-1 and BHV-1 gB were made but they could be distinguished immunologically by monoclonal antibodies. Both glycoproteins were inserted into cellular and virion membranes but did not form oligomers with each other. A monoclonal antibody that binds to HSV-1 gB but not BHV-1 gB neutralized the parental HSV-1 and a revertant Pseudodiploid virus from which the gene encoding BHV-1 gB had been excised, but was significantly less efficient at neutralizing the Pseudodiploid viruses. This suggests that the BHV-1 homologue can complement the HSV-1 gB functions required for infectivity.
Teemu P. Miettinen - One of the best experts on this subject based on the ideXlab platform.
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Mass measurements during lymphocytic leukemia cell polyploidization decouple cell cycle- and cell size-dependent growth.
Proceedings of the National Academy of Sciences of the United States of America, 2020Co-Authors: Joon Ho Kang, Selim Olcum, Kristofor R. Payer, Nicholas L. Calistri, Robert J. Kimmerling, Scott R. Manalis, Teemu P. MiettinenAbstract:Cell size is believed to influence cell growth and metabolism. Consistently, several studies have revealed that large cells have lower mass accumulation rates per unit mass (i.e., growth efficiency) than intermediate-sized cells in the same population. Size-dependent growth is commonly attributed to transport limitations, such as increased diffusion timescales and decreased surface-to-volume ratio. However, separating cell size- and cell cycle-dependent growth is challenging. To address this, we monitored growth efficiency of Pseudodiploid mouse lymphocytic leukemia cells during normal proliferation and polyploidization. This was enabled by the development of large-channel suspended microchannel resonators that allow us to monitor buoyant mass of single cells ranging from 40 pg (small Pseudodiploid cell) to over 4,000 pg, with a resolution ranging from ∼1% to ∼0.05%. We find that cell growth efficiency increases, plateaus, and then decreases as cell cycle proceeds. This growth behavior repeats with every endomitotic cycle as cells grow into polyploidy. Overall, growth efficiency changes 33% throughout the cell cycle. In contrast, increasing cell mass by over 100-fold during polyploidization did not change growth efficiency, indicating exponential growth. Consistently, growth efficiency remained constant when cell cycle was arrested in G2. Thus, cell cycle is a primary determinant of growth efficiency. As growth remains exponential over large size scales, our work finds no evidence for transport limitations that would decrease growth efficiency.
Steven R. King - One of the best experts on this subject based on the ideXlab platform.
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Pseudodiploid genome organization AIDS full-length human immunodeficiency virus type 1 DNA synthesis.
Journal of virology, 2007Co-Authors: Steven R. King, Nisha K. Duggal, Clement B. Ndongmo, Crystal Pacut, Alice TelesnitskyAbstract:Template switching between copackaged human immunodeficiency virus type 1 (HIV-1) genomic RNAs is genetically silent when identical RNAs are copackaged but yields recombinants when virions contain two distinct RNAs. Sequencing has revealed that errors at retroviral recombination junctions are infrequent, suggesting that template switching is not intrinsically mutagenic. Here, we tested the hypothesis that template switching may instead contribute to replication fidelity. This hypothesis predicts that reverse transcription of a single-copy gene will be more error prone than replication in the presence of a second copy. To test this, HIV-1-based vectors containing both lacZ and the puromycin resistance marker were expressed either alone or with an excess of an "empty" vector lacking lacZ and puro. This resulted in virions with either RNA homodimers or haploid genomes with only a single lacZ-puro RNA. In untreated cells, lacZ inactivation rates suggested that haploid vector reverse transcription was slightly more error prone than that of homodimerized Pseudodiploid vectors. Haploid reverse transcription was at least threefold more error prone than Pseudodiploid-templated synthesis when slowed by hydroxyurea treatment or stopped prematurely with zidovudine. Individual products of one- and two-copy genes revealed both nucleotide substitutions and deletions, with deletions more frequent than point mutations among haploid genome products. Similar spectra of defective products were observed at early reverse transcription time points and among products of haploid virions. These results indicate that faithful, full-length reverse transcription products were underrepresented in the absence of a reserve of genetic information and suggest that template switching contributes to HIV-1 genomic integrity.
