Map location of the pcbA mutation and physiology of the mutant

Abstract

Many temperature-resistant revertants of a polAl polB polCts (HS432) strain are PolI+ (by either suppression of the polAl amber allele or intragenic reversion) but remain polCts (contain a temperaturesensitive DNA polymerase III). It appears that DNA replication in such temperature-resistant revertants depends on an extragenic mutation, pcbA, already present in the parent strain and not linked to any of the DNA polymerase loci. This allele allows DNA replication dependent on DNA polymerase I and bypasses a temperature-sensitive DNA polymerase III (polC bypass), so that reversion to PolI+ makes the strain temperature resistant. This pathway of DNA replication also supports phage and plasmid DNA replication. At restrictive temperature, these mutants display a normal response to UV irradiation but show increased sensitivity to the alkylating agent methyl methanesulfonate. We have located pcbA linked to dnaA.