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Revision as of 20:27, 7 February 2008
SsrA-mediated tagging and proteolysis of LacI and its role in the regulation of lac operon
- SsrA RNA (also known as 10sRNA or tmRNA) acts as both mRNA and tRNA when ribosomes are paused at 3’ end of an mRNA lacking a stop codon.
- Trans-translation process (mediated by SsrA RNA) leads to addition of C-term tag to polypeptide. Tagged peptide is then degraded by specific proteases.
- Major biological relevance of SsrA-mediated tagging and proteolysis is believed to be in providing both a way to clear the ribosome stalled on mRNAs and a quality-control mechanism that allows cell to eliminate potentially harmful truncated polypeptides.
- For example: the binding of LacI to the lac operators results in truncated lacI mRNAs that are tagged/degraded by the SsrA trans-translation system. (note: in presence of IPTG, IPTG binds LacI repressor s.t. LacI repressor doesn’t bind operators and LacI mRNAs are not truncated or tagged/degraded)
Micros for microbes: non-coding regulatory RNAs in bacteria
- small non-coding RNAs with important regulatory roles are not confined to eukaryotes
- they act post-transcriptionally, imposing a regulatory step that is independent of and epistatic to transcriptional signals.
- they act by base-pairing with target mRNAs, resulting in changes in the translation and stability of the mRNA.