The full form of tmRNA is Transfer-messenger RNA.
tmRNA, also written as transfer-messenger RNA, is a unique bacterial RNA molecule that possesses properties of both tRNA (transfer RNA) and mRNA (messenger RNA). It's also known as 10Sa RNA and by its genetic name, SsrA. It plays a critical role in a process called trans-translation, which rescues ribosomes stalled on damaged mRNA or mRNAs lacking a stop codon. This prevents the accumulation of non-functional proteins and ensures proper protein quality control within the bacterial cell.
Here's a breakdown of why tmRNA is important:
- Dual Functionality: It acts as both a tRNA by initially being charged with alanine, and as mRNA by containing a short open reading frame (ORF) that encodes a degradation tag.
- Ribosome Rescue: When a ribosome is stalled on a mRNA lacking a stop codon, tmRNA enters the A-site of the ribosome.
- Trans-Translation: The ribosome switches from translating the original, faulty mRNA to translating the ORF on the tmRNA. This adds a short peptide tag to the C-terminus of the partially synthesized protein.
- Protein Degradation: This peptide tag serves as a signal for cellular proteases to degrade the incomplete and potentially harmful protein.
- mRNA Degradation: Often, the mRNA that caused the stalling is also targeted for degradation.
In summary, tmRNA is a crucial component of bacterial protein quality control, ensuring that aberrant or incomplete proteins are eliminated, and the ribosomes involved in their production are freed up for further protein synthesis.
