The TraM protein of the conjugative plasmid F binds to the origin of transfer of the F and ColE1 plasmids

The gene encoding the TraM protein of the conjugative plasmid F was cloned, overexpressed and the gene product was purified. The TraM protein was found in the cytoplasm of cells carrying the F plasmid with a smaller amount in the inner membrane. DNase I footprinting experiments showed that the purified protein protects three regions in the F oriT locus with different affinity for the upper and lower strands of DNA. A 15-nucleotide motif was identified within the protected regions that represented the DNA-binding site. The TraM protein was also found to bind to a sequence in the oriT region of the non-conjugative plasmid ColE1 that resembles the three binding sites in the F oriT region.