The TraM protein is an essential part of the DNA transfer machinery of the conjugative resistance plasmid R1 (IncFII). On the basis of mutational analyses, it was shown that the essential transfer protein TraM has at least two functions. First, a functional TraM protein was found to be required for normal levels of transfer gene expression. Second, experimental evidence was obtained that TraM stimulates efficient site-specific single-stranded DNA cleavage at the oriT, in vivo. Furthermore, a specific interaction of the cytoplasmic TraM protein with the membrane protein TraD was demonstrated, suggesting that the TraM protein creates a physical link between the relaxosomal nucleoprotein complex and the membrane-bound DNA transfer apparatus.