Search

M1 RNA, the gene product of rnpB, is the catalytic subunit of RNase P in Escherichia coli. M1 RNA is transcribed from a proximal promoter as pM1 RNA, a precursor M1 RNA, and then is processed at its 3' end by RNase E. In addition to pM1 RNA, large rnpB-containing transcripts are produced from unknown upstream promoters. However, it is not known yet how these large transcripts contribute to M1 RNA biosynthesis. To examine their biological relevance to M1 RNA biosynthesis, we constructed a model upstream transcript, upRNA, and analyzed its cellular metabolism. We found that upRNA was primarily degraded rather than processed to M1 RNA in the cell and that this degradation occurred in RNase E-dependent manner. The in vitro cleavage assay with the N-terminal catalytic fraction of RNase E showed that the M1 RNA structural sequence in upRNA was much more vulnerable to the enzyme than the sequence in pM1 RNA. Considering that RNase E is a processing enzyme involved in 3' end formation of M1 RNA, our results imply that this enzyme plays a dual role in processing and degradation to achieve tight control of M1 RNA biosynthesis.

Initiation factor 1 (IF1) is an essential protein in Escherichia coli involved in the initiation step of protein synthesis. The protein level of IF1 increases when E. coli cells are subjected to cold shock, however, it remains unclear as to how this increase occurs. The infA gene encoding IF1 contains two promoters, the distal P1 and the proximal P2 promoter. In this study, we found that infA mRNA was greatly increased, and that this increase resulted from transcriptional activation of P1, not P2, during cold shock although stability of transcripts from both promoters concomitantly increased.