Transcriptional analysis of the F plasmid surface exclusion region: mapping of traS, traT, and traD transcripts.

Transcription of the surface exclusion genes, traS and traT, of the F plasmid of Escherichia coli K-12 has been analyzed using S1 nuclease protection experiments. The results show that both genes possess functional promoters in vivo and that a strong transcriptional termination signal lies immediately downstream of traT. Moreover, the adjacent downstream gene, traD, is expressed from its own promoter and appears not to lie within the major transfer operon. RNA stability experiments indicate that the products of traS and traT are translated from a stable RNA message. We propose that the traS and traT promoters serve to supplement the expression of these genes from the major tra promoter, PY.