Transcription start sites in the promoter region of the Escherichia coli pcnB (plasmid copy number) gene coding for poly(A) polymerase I.

Escherichia coli pcnB gene was discovered as a regulator of ColE1 plasmid copy number about 20 years ago. Further studies indicated that this gene codes for poly(A) polymerase I (PAP I). However, although importance of RNA polyadenylation has been demonstrated and biochemical properties of PAP I have been studied extensively, little is known about regulation of the pcnB gene transcription. Here, we demonstrate that there are three transcription start sites upstream of the pcnB coding sequence. Activities of at least two of these promoters were in inverse correlation to bacterial growth rates, which agrees with recently published results indicating increased abundance of PAP I and higher levels of RNA polyadenylation in slowly growing bacteria.