Excision of pyrimidine dimers in normal and T4-infected Escherichia coli: effect of polA and other mutations.

Strains carrying both polA1 and recBts1 mutations, which are defective in DNA polymerase I and have thermolabile exonuclease V (the recBC enzyme), are viable at 30 degrees C but not at 42 degrees C. These mutants exhibit almost normal rate of dimer excision in vivo even at the restrictive temperature. Similar results were obtained with other polA minus strains. We have also investigated effect of host and phage mutations on excision of dimers in T4-infected cells. Only a small amount of dimer is excised in T4v-1-infected cells whereas an extensive and selective release of dimers takes place in T4D-infected cells. Other phage mutations, including mutations in gene 43 and gene 30, do not affect excision of dimers in infected cells.