Regulation of the F conjugation genes studied by hybridization and tra-lacZ fusion

Hybridization experiments and tra-lacZ fusions were used to obtain further insight into the complex series of control systems that affect F conjugation. We confirmed that the regular IncF FinOP control system represses transcription of traJ, and found that the traJ product is required for transcription of traM as well as of the traY-Z operon. The chromosomal sfrA gene product may be required to prevent premature termination of traJ transcription, while the sfrB gene product prevents premature termination at two sites within the traY-Z operon. The FinQ inhibition system determined by several IncI plasmids caused termination at three different sites in the operon, and that of JR66a at one further site. JR66a and R485 strongly inhibit F transfer, but have weak, or no (respectively) effects on transcription: they may inhibit function of one or more transfer gene products.