AUTORADIOGRAPHIC STUDY OF TRANSFER OF DNA DURING BACTERIAL CONJUGATION

Amounts of H(3)-thymine-labeled DNA that are transferred from cell to cell in Hfr x F(-) and F(+) x F(-) matings have been measured autoradiographically. The transferred amounts are compared to the DNA content of the bacterial chromosome, which was measured autoradiographically on the basis of a model for the replication of DNA in E. coli (1). Partition of transferred radioactivity among the progeny of F(-) exconjugants was also observed by autoradiography. When F(+) donors were used, it was found that the transferred label often remained intact during growth of the recipients into microcolonies. The class of colonies in which this occurred was shown to contain a uniform amount of radioactivity amounting to 0.5 to 0.9 per cent of the bacterial chromosome. Dispersal of the radioactivity into smaller units was also observed. The fraction of females receiving F from F(+) donors, as measured genetically, was close to the fraction of females receiving DNA-label. The distributions of amounts of radioactivity transferred to females by Hfr males after different periods of mating were shown to fit the predictions of genetic analysis of chromosomal transfer-on the assumption that the total genetic map corresponds to the whole bacterial chromosome. The label transferred by Hfr donors was found to be variably dispersed among the progeny (4 to 5 generations) of the recipient cells.