The hydrophobic TraM protein of pKM101 is required for conjugal transfer and sensitivity to donor-specific bacteriophage.

pKM101 is a self-transmissible plasmid of the IncN incompatibility group. Analysis of the DNA sequences of the genes required for conjugal transfer suggested the existence of a previously uncharacterized open reading frame, designated traM, that might be required for conjugation. Merodiploid strains containing transposon insertion mutations either in traM or in neighboring tra genes were used to demonstrate that traM constitutes a new complementation group essential for conjugation and donor phage sensitivity. The hydrophobicity profile of TraM suggests that it contains a signal sequence. The remainder of TraM is also composed predominantly of hydrophobic amino acids but contains one possible surface exposed loop. TraM-alkaline phosphatase and TraM-beta-galactosidase fusion proteins supported the hypothesis that TraM has a small cytoplasmic loop. We were unable to detect heterologous complementation between any tra mutation and its homolog from the virB operon of Agrobacterium tumefaciens.