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Abstract
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.
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