title: Proof-reading 3'-->5' exonucleases isolated from rat liver nuclei.
abstract: Mammalian nuclear DNA polymerases alpha and beta are known to be devoid of the editing 3'-->5' exonucleolytic activity. Presumably this activity could be effected by the exonucleases non-associated covalently with DNA polymerases. Two 3'-->5' exonucleases of 40 kDa and 50 kDa (exo-40 and exo-5) have been isolated from rat liver nuclei and purified to near homogeneity. They are shown to excise mismatched nucleotides from poly[d(A-T)] template, respectively, 10-fold and 2-fold faster than the matched ones. Upon addition of either of these exonucleases to the DNA polymerase alpha from rat liver or calf thymus, the fidelity of in-vitro reproduction of the primed DNA from bacteriophage phi X174 amber 3 is increased 5-10-fold, levels of exonuclease and DNA-polymerase activities being similar. Extrapolation of in-vitro DNA-replication fidelity to the cellular levels of activities of the exonucleases and the alpha-polymerase suggests that exonucleolytic proof-reading augments the accuracy of DNA synthesis by 2-3 orders of magnitude.
authors.affiliation: Department of Molecular and Radiation Biophysics, Petersburg Nuclear Physics Institute, Russia Academy of Sciences, Gatchina.
authors.forename: N V
authors.initials: NV
authors.lastname: Belyakova
authors.forename: N E
authors.initials: NE
authors.lastname: Kleiner
authors.forename: T P
authors.initials: TP
authors.lastname: Kravetskaya
authors.forename: O K
authors.initials: OK
authors.lastname: Legina
authors.forename: S N
authors.initials: SN
authors.lastname: Naryzhny
authors.forename: F W
authors.initials: FW
authors.lastname: Perrino
authors.forename: I V
authors.initials: IV
authors.lastname: Shevelev
authors.forename: V M
authors.initials: VM
authors.lastname: Krutyakov
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002467:Cell Nucleus / Q000201:enzymology; D004247:DNA / Q000096:biosynthesis*; D004257:DNA Polymerase II / Q000378:metabolism*; D005092:Exonucleases / Q000302:isolation & purification / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008297:Male; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011067:Poly dA-dT / Q000378:metabolism; D051381:Rats
chemical_list: D011067:Poly dA-dT; D004247:DNA; D004257:DNA Polymerase II; D005092:Exonucleases