Which specific RNA is recruited to the site of incomplete or broken mRNAs to save ribosomes?

tmRNA, or transfer-messenger RNA, plays a critical role in rescuing ribosomes that are stalled on incomplete or broken mRNAs during protein synthesis. When a ribosome encounters a non-stop codon or incomplete mRNA that lacks a proper termination signal, it cannot release the polypeptide chain properly and can become trapped on the mRNA.

tmRNA serves as a unique molecule that combines features of both tRNA and mRNA. It provides a means for the ribosome to read through the defective mRNA and continue translating. The tmRNA carries a short coding sequence that encodes a tagged peptide, which is pivotal because it signals the cellular machinery to recognize and degrade the faulty mRNA. In this way, tmRNA not only helps to free the ribosome but also ensures that the remnants of the non-functional mRNA are disposed of properly, promoting overall cellular efficiency.

This process is essential for maintaining ribosome function and preventing the accumulation of stalled ribosomes in the cell, which could lead to further complications in protein synthesis.