SsrA, or tmRNA, is a small RNA found in all bacteria that intervenes in selected translation reactions to target the nascent polypeptide for rapid proteolysis. We have found that the abundance of SsrA RNA in Caulobacter crescentus is regulated with respect to the cell cycle. SsrA RNA abundance increases in late G1 phase, peaks during the G1-S transition, and declines in early S phase, in keeping with the reported role for SsrA in the timing of DNA replication initiation. Cell cycle regulation of SsrA RNA is accomplished by a combination of temporally controlled transcription and regulated RNA degradation. Transcription from the ssrA promoter peaks late in G1, just before the peak in SsrA RNA abundance. SsrA RNA is stable in G1-phase cells and late S-phase cells but is degraded with a half-life of 4 to 5 min at the onset of S phase. This degradation is surprising, since SsrA RNA is both highly structured and highly abundant. This is the first observation of a structural RNA that is cell cycle regulated.
All Science Journal Classification (ASJC) codes
- Molecular Biology