Mechanisms of error discrimination by Escherichia coli DNA polymerase I.
The mechanism of base selection by DNA polymerase I of Escherichia coli has been investigated by kinetic analysis. The apparent KM for the insertion of the complementary nucleotide dATP into the hook polymer poly(dT)-oligo(dA) was found to be 6-fold lower than that for the noncomplementary nucleotide dGTP, whereas the Vmax for insertion of dATP was 1600-fold higher than that for dGTP. The ratio of Kcat/KM values for complementary and mismatched nucleotides of 10(4) demonstrates the extremely high specificity of base selection by DNA polymerase I and is in agreement with results obtained with a different template-primer, poly(dC)-oligo(dG) [El-Deiry, W. S., Downey, K. M., & So, A. G. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 7378]. Studies on the effects of phosphate ion on the polymerase and 3'- to 5'-exonuclease activities of DNA polymerase I showed that, whereas the polymerase activity was somewhat stimulated by phosphate, the exonuclease activity was markedly inhibited, being 50% inhibited at 25 mM phosphate and greater than 90% inhibited at 80 mM phosphate. Selective inhibition of the exonuclease activity by phosphate also resulted in inhibition of template-dependent conversion of a noncomplementary dNTP to dNMP and, consequently, markedly affected the kinetic constants for insertion of noncomplementary nucleotides. The mutagenic metal ion Mn2+ was found to affect error discrimination by both the polymerase and 3'- and 5'-exonuclease activities of DNA polymerase I.(ABSTRACT TRUNCATED AT 250 WORDS)
el-Deiry
W S
WS
Department of Medicine, University of Miami School of Medicine, Florida 33101.
So
A G
AG
Downey
K M
KM
D001483:Base Sequence; D004256:DNA Polymerase I / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D009994:Osmolar Concentration; D013379:Substrate Specificity; D013698:Templates, Genetic
D008345:Manganese; D004256:DNA Polymerase I; D008274:Magnesium