ALTERNATE PATHWAYS OF DNA-REPLICATION - DNA POLYMERASE-I-DEPENDENT REPLICATION

Some Escherichia coli strain HS432 derivatives (polA1, polB100, polC1026) can replicate DNA at a restrictive temperature in the presence of a polCts mutation. These revertants appear to have DNA polymerase I activity. E. coli strain HS432 becomes temperature-resistant on the introduction of a normal gene for DNA polymerase I or on suppression of the polA1 nonsense mutation. Such temperature-resistant phenocopies become temperature-sensitive on introduction of a temperature-sensitive DNA polymerase I gene. DNA replication is thus DNA polymerase I-dependent in the temperature-resistant revertants, indicating that an alternative pathway of replication exists in E. coli. HS432 contains a transducible locus (termed pcbA) that can support an alternate pathway in other E. coli strains, suggesting that the effect of suppression of polCts is a general one.