Sense and antisense transcripts of traM, a conjugal transfer gene of the antibiotic resistance plasmid R100

The region of the antibiotic resistance plasmid R100 that encodes the plasmid-specific transfer gene traM has two tandemly aligned promoters separated by 145 nucleotides. The principal transcripts are 705 and 562 nucleotides long. Minor transcripts are 1550 and 1700 nucleotides long. The 705-base transcript appears to encode an 11 kD traM protein. The 562-base transcript does not encode a detectable protein. When subcloned on short fragments, the promoter for the 562-base transcript initiates efficiently but that for the 705 site does not. The 3' ends of the 705 and 562 base transcripts end inside the traJ ORF. Thus they provide additional sense RNA to compete with traJ for finP, the antisense translational regulator of traJ. A model is proposed for the participation of these sense and antisense transcripts in the control of expression of the traJ gene.