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Conjugation in Escherichia coli: Difference in the molecular mechanism of F self-transmission and Hfr transfer

There is a large group of plasmids with chromosome mobilizing activity. The first reported and most studied is the F factor. Within its host bacterium, F can exist in two different states. In one state, it behaves as an autonomous, cytoplasmic element. At conjugation, it promotes its own transfer to the recipient (F´ self-transmission). In its alternative state, F is integrated into the chromosome. At conjugation, it promotes transfer of the bacterial genes to the recipient (Hfr transfer). According to the longstanding doctrine, the molecular mechanism of Hfr transfer is essentially the same as that of F´self-transmission. Our recent results have showed that, at least in the case of a commonly used strain 3000, Hfr transfer , unlike F´ self-transmission, requires the presence of the functional RecBCD enzyme. We propose one version of the double-strand break repair model to explain this result.

Escherichia coli; F plasmid; Hfr transfer; RecBCD enzyme

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