Thymine Starvation and Genetic Damage in Escherichia coli

SUMMARY: Two thy - Hfr strains of Escherichia coli K12 were mated with stationary phase W677 F- at intervals during thymine starvation. With both strains, Hfr bacteria retained their capability of chromosome transfer for a period after loss of colony-forming ability. Eventual loss of transfer capability in strain HfrC thy - was associated with inactivation of some early stage of the transfer process. Thymine starved HfrC thy - transferred the genetic markers pro, thr, leu and thi with a normal gradient but HfrB1 thy - showed marker inactivation. The extent of marker inactivation in this strain was consistent with the presence of 10-20 breaks/chromosome. It is suggested that the strains may have behaved differently in these experiments as a result of differences in their ability to modify primary genetic lesions resulting from thymine starvation.