Dependence of efficiency of DNA transfer and recombinat formation on cell cycle of Hfr in Escherichia coli K-12.

The efficiency of DNA transfer during the Hfr cell cycle, studied with the use of 3H-thymidine, is the highest in the first half of the cycle. The efficiency of recombinant formation in the Hfr cell cycle demonstrates a similar periodicity only when the ratio of 1 Hfr cell to 8 or more F- cells in mating mixture is maintained. The absence of such changes in the number of recombinants during the cell cycle of a donor with relative excess of Hfr cells seems to be caused by limitation of the number of recombinants by the competent recipent cell fraction.