title: Roles of host cell factors in circularization of retroviral dna.
abstract: Early during retroviral infection, a fraction of the linear reverse-transcribed viral DNA genomes become circularized by cellular enzymes, thereby inactivating the genomes for further replication. Prominent circular DNA forms include 2-long-terminal repeat (LTR) circles, made by DNA end joining, and 1-LTR circles, produced in part by homologous recombination. These reactions provide a convenient paradigm for analyzing the cellular machinery involved in DNA end joining in vertebrate cells. In previous studies, we found that inactivating components of the nonhomologous DNA end-joining (NHEJ) pathway--specifically Ku, ligase 4, or XRCC4--blocked formation of 2-LTR circles. Here we report that inactivating another NHEJ component, the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), had at most modest effects on 2-LTR circle formation, providing informative parallels with other end-joining reactions. We also analyzed cells mutant in components of the RAD50/MRE11/NBS1 nuclease and found a decrease in the relative amount of 1-LTR circles, opposite to the effects of NHEJ mutants. In MRE11-mutant cells, a MRE11 gene mutant in the nuclease catalytic site failed to restore 1-LTR circle formation, supporting a model for the role of MRE11 in 1-LTR circle formation. None of the cellular mutations showed a strong effect on normal integration, consistent with the idea that the cellular pathways leading to circularization are not involved in productive integration.
mesh_terms: D018797:Cell Cycle Proteins / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair; D004270:DNA, Circular / Q000378:metabolism*; D004706:Endodeoxyribonucleases / Q000378:metabolism; D005090:Exodeoxyribonucleases / Q000378:metabolism; D015497:HIV-1 / Q000235:genetics* / Q000472:pathogenicity; D006801:Humans; D034982:Integration Host Factors / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D016662:Virus Integration
chemical_list: D018797:Cell Cycle Proteins; D004270:DNA, Circular; D034982:Integration Host Factors; C112156:NBN protein, human; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; D004247:DNA; D011494:Protein Kinases; D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases; C094191:MRE11 protein, S cerevisiae