Ar. Oller et Rm. Schaaper, SPONTANEOUS MUTATION IN ESCHERICHIA-COLI CONTAINING THE DNAE911 DNA-POLYMERASE ANTIMUTATOR ALLELE, Genetics, 138(2), 1994, pp. 263-270
We have previously isolated mutants of Escherichia coli that replicate
their DNA with increased fidelity. These mutants have a mutation in t
he dnaE gene, encoding the cu subunit of DNA polymerase III. They were
isolated in a mismatch-repair-defective mutL background, in which mut
ations can be considered to represent uncorrected DNA replication erro
rs. In the present study we analyze the effect of one of these alleles
, dnaE911, an spontaneous mutagenesis in a mismatch-repair-proficient
background. In this background, spontaneous mutations may be the sum o
f uncorrected replication errors and mutations resulting from other pa
thways. Hence, the effect of the dnaE allele may provide insights into
the contribution of uncorrected DNA replication errors to spontaneous
mutation. The data show that dnaE911 decreases the level of Rifr, lad
and galK mutations in this background by 1.5-2-fold. DNA sequencing o
f 748 forward mutants in the lad gene reveals that this effect has a c
lear specificity. Transversions are decreased by similar to 3-fold, wh
ereas transitions, frameshifts, deletions and duplications remain esse
ntially unchanged. Among the tranversions, A.T --> T.A are affected mo
st strongly (similar to 6-fold). In addition to this effect on transve
rsions within the lacI gene, one previously recognized A.T --> G.C bas
e-pair substitution hotspot in the lac operator is also reduced (simil
ar to 5-fold). The data are discussed in the light of the role of DNA
replication errors in spontaneous mutation, as well as other possible
explanations for the observed antimutator effects.