Genetic and physiological characterization of a spontaneous mutant of Escherichia coli B/r with aberrant control of deoxyribonucleic acid replication.

Strain TJK16, a low-thymine-requiring thyA deoB derivative of Escherichia coli B/r A, was found to have an increased initiation mass due to a mutation in a gene affecting the control of initiation of deoxyribonucleic acid replication. In contrast to temperature-sensitive initiation mutants, initiation in TJK16 was not temperature sensitive. By phage P1 transduction, it was found that the mutation lies within a small region of the chromosome between dnaA and gyrB; this region includes dnaN and recF. Coumermycin-resistant derivatives of B/r and TJK16 had the same initiation mass as their coumermycin-sensitive parents, and TJK16 had the same sensitivity to coumermycin as the B/r parent, suggesting that the initiation mutation is not in gyrB.