Initiation, attenuation and RNase III processing of transcripts from the XXXX operon encoding ribosomal protein S15 and polynucleotide phosphorylase.

@entity526 @entity2036
The rpsO gene of @entity526 , which encodes ribosomal protein S15 is located at 69 minutes on the chromosome. It is adjacent to the pnp gene, which encodes polynucleotide phosphorylase. The two genes are separated by 249 @entity2036 and are transcribed in the same direction. We report here in vivo S1 nuclease mapping and in vitro transcription experiments that demonstrate that rpsO and pnp are cotranscribed from a promoter P1, located 108 @entity2036 upstream from rpsO, and that another promoter P2, located between the two genes 158 @entity2036 upstream from pnp, also directs the transcription of pnp. Transcription from P1 can either terminate at the terminator t1 identified in vivo and in vitro, 18 @entity2036 downstream from rpsO, or transcribe through t1 and into pnp. Comparison of the transcripts synthesized in wild-type and RNase III-deficient strains of @entity526 shows that all the P1 readthrough transcripts and P2 transcripts are cleaved by RNase III. Two specific cuts are made by RNase III in a double-stranded structure about 100 @entity2036 upstream rpsO. We also found that some transcripts of this operon start 47 @entity2036 downstream from rpsO, in the region of t1. No promoter has been identified in this region. This mRNA is attributed to an endonucleolytic cleavage of the polycistronic transcripts and the location of the cut is named M. The order of the transcription signals and of the maturation sites in relation to rpsO and pnp can be summarized as follows: P1, rpsO, t1, M, P2, RNase III-processing sites, pnp. The possible roles of mRNA processing events in the expression of rpsO-pnp operon are discussed.
