tmRNA is a bacterial RNA molecule with dual tRNA-like and mRNA-like properties. It forms an RNA-protein complex with ribosomal protein S1, elongation factor Tu, and the dedicated protein SmpB.
This complex enters ribosomes that have stalled during protein elongation and promotes: i) rescue of the stalled ribosomes, ii) degradation of the problematic mRNA, and iii) extension of the unfinished polypeptide, first with the alanine charging tmRNA and then with the proteolysis-inducing tag encoded by tmRNA.
Most bacteria encode a standard one-piece tmRNA. In other bacterial species, a permuted tmRNA gene produces a two-piece tmRNA in which two separate RNA chains are joined by base-pairing.
The current (22-Oct-2013) database contains 1631 unique sequences and links these to 12509 instances in GenBank/EMBL-EBI/DDBJ (INSDC) entries that comprise 7590 taxa.