Regulation of R100 conjugation requires traM in cis to traJ

Deletion mutants of R100-1 were constructed by classical methods to remove various segments of the traM open reading frame, pTraM-binding sites and the traM promoters. Complementation tests showed that traM was efficiently complemented only when the trans-acting fragment contained both the complete traM gene and the adjacent traJ promoter and leader sequences. The conclusion is that traM and traJ constitute a complex operon. A deletion mutant lacking all of the traJ gene, and one containing a frameshifting traM deletion, retained the ability to transfer at a low level, thereby showing that neither pTraM nor pTraJ is absolutely essential for transfer.