text: In bacteria, trans-translation, a highly conserved mechanism, acts as a direct counter to the accumulation of non-stop RNA, inducing decay and liberating the misregulated ribosome.  Originally discovered in Escherichia coli, the process of trans-translation is made possible by the interactions between transfer-messenger RNA (tmRNA) and the cofactor protein SmpB, which allows for the stable binding of the tmRNA to the stalled ribosome.  The current tmRNA model states that tmRNA and SmpB interact together in order to mimic tRNA.  The SmpB protein recognizes the point of stalling, and directs the tmRNA to bind to the ribosomal A site. Once bound, SmpB engages in a transpeptidation reaction with the improperly functioning polypeptide chain through the donation of charged alanine.  Through this process, the stalled and defective mRNA sequence is replaced with the SmpB RNA sequence, which encodes for the addition of an 11 amino acid tag on the C-terminus of the mRNA, which promotes degradation.  The modified portion of RNA, along with the amino acid tag, are translated, and demonstrate incomplete characteristics, alerting and allowing for intracellular proteases to remove these harmful protein fragments, causing stalled ribosomes on damaged mRNA to resume function.