GENE TRANSFER BY F′ STRAINS OF ESCHERICHIA COLI K-12 I. : Delay in Initiation of Chromosome Transfer1

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Pittard, James (Yale University, New Haven, Conn.), John S. Loutit, and Edward A. Adelberg. Gene transfer by F′ strains of Escherichia coli K-12. I. Delay in initiation of chromosome transfer. J. Bacteriol. 85:1394–1401. 1963.—Two different F′ strains were found to transfer both F-merogenote and chromosomal markers to recipient strains. When zygotes having received different chromosomal markers from the male were selected, a high percentage of them were found to have also received F-merogenote markers under conditions in which the mating of more than one male cell with a single female cell was excluded. An analysis of the kinetics of zygote formation revealed that chromosomal markers began to be transferred from F′ strains 8 to 10 min later than from their analogous Hfr strains. The rate of chromosome transfer is the same from both F′ and Hfr strains, and the difference observed in kinetic experiments was shown not to be due to any difference between the sequence of chromosomal genes in the F′ and Hfr strains. F′ strains and Hfr strains showed no difference in ability to form specific pairs with female recipients shortly after mixing. The observed delay in the transfer of chromosomal markers from F′ cells thus means that, after specific pair formation, F′ cells take 8 to 10 min longer than Hfr cells to initiate chromosome transfer.

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