Transcription of the transfer genes traY and traM of the antibiotic resistance plasmid R100-1 is linked

Three separate traY deletion mutants of R100-1 were prepared by allele repl acement. These mutants retained the ability to transfer at a level 100 time s greater than R100 and 1/50 that of the parental R100-1. The mutants were complemented to normal R100-1 transfer levels by pDSP06, a multicopy traY c lone. Comparison of transcripts initiated at the traY promoter, P-Y, by pri mer extension experiments showed that there was no detectable P-Y, activity in R100 and that the level of P-Y activity in the traY deletion mutants wa s lower than that in R100-1. Similar measurements performed on RNA from a s et of previously described traM deletion mutants showed that those traM del etion mutants that produced more traM and finM (M) transcripts than the par ental R100-1 also produced more traY transcripts than R100-1 and that those traM mutants that produced fewer M transcripts than R100-1 also produced f ewer traY transcripts than R100-1. We conclude that in R100, TraY regulates P-Y activity and that transcripts originating in traM affect P-Y activity.