title: 'External' proofreading of DNA replication errors and mammalian autonomous 3'-->5'exonucleases.
abstract: Mammalian nuclear DNA polymerases alpha and beta are known to be devoid of the editing 3'-->5' exonucleolytic activity. The base substitutions misinserted by these polymerases could be eliminated with two kinds of an 'external' proofreading carried out (1) by the 3'-->5' exonuclease function intrinsic to DNA polymerases delta and epsilon or/and (2) by the autonomous 3'-->5' exonucleases non-associated covalently with DNA polymerases. DNA polymerases delta and epsilon can be separated from autonomous 3'-->5' exonucleases by means of sedimentation. Ultracentrifugation of the nuclear extracts and cytosols from normal and regenerating rat liver as well as from total embryos has shown the bulk of the cellular 3'-->5' exonucleolytic activity is due to autonomous nucleases. Moreover, the level of such a specific activity correlates with the replicative status of the organs from adult animals: spleen > regenerating liver > normal liver > cardiac muscle > brain, maximum difference being an order of magnitude. In addition, autonomous exonucleases were shown to be the constituents of the multienzyme forms of DNA polymerases alpha and beta. Hence, autonomous 3'-->5' exonucleases seem to be the principal participants in an 'external' proofreading.
authors.affiliation: Department of Molecular and Radiation Biophysics, Petersburg Nuclear Physics Institute of the Russia Academy of Sciences, Gatchina, Leningrad District, Russia.
authors.forename: I V
authors.initials: IV
authors.lastname: Shevelev
authors.forename: T P
authors.initials: TP
authors.lastname: Kravetskaya
authors.forename: O K
authors.initials: OK
authors.lastname: Legina
authors.forename: V M
authors.initials: VM
authors.lastname: Krutyakov
mesh_terms: D000818:Animals; D002457:Cell Extracts; D002467:Cell Nucleus / Q000201:enzymology; D004256:DNA Polymerase I / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D004257:DNA Polymerase II / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D004258:DNA Polymerase III; D004261:DNA Replication / Q000502:physiology*; D004259:DNA-Directed DNA Polymerase / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D004622:Embryo, Mammalian / Q000201:enzymology; D043211:Exodeoxyribonuclease V; D005090:Exodeoxyribonucleases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008099:Liver / Q000201:enzymology; D008970:Molecular Weight; D009928:Organ Specificity; D051381:Rats
chemical_list: D002457:Cell Extracts; D004256:DNA Polymerase I; D004257:DNA Polymerase II; D004258:DNA Polymerase III; D004259:DNA-Directed DNA Polymerase; D005090:Exodeoxyribonucleases; D043211:Exodeoxyribonuclease V