ribosomemRNAnascent

ribosomemRNAnascent is the transient complex formed during translation when a ribosome engages an mRNA transcript and begins synthesizing a nascent polypeptide. The complex includes the ribosome, the messenger RNA, and the nascent polypeptide tethered to a tRNA at the peptidyl transferase site. As codons are read, aminoacyl-tRNAs enter the A site, the growing chain is transferred to the P site, and the ribosome translocates along the mRNA. The nascent chain remains linked to the tRNA until termination.

In eukaryotes, some nascent chains are targeted to the endoplasmic reticulum as they emerge. The signal recognition particle recognizes signal peptides, pauses translation, and directs the ribosome to the ER translocon where translocation into the ER lumen or membrane insertion occurs. Other nascent chains stay in the cytosol, aided by cytosolic chaperones and ribosome-associated factors that promote proper folding.

RibosomemRNAnascent complexes are studied to understand translation kinetics, cotranslational folding, and proteostasis. Techniques include ribosome profiling (Ribo-Seq) to map ribosome positions on mRNA and affinity purification of ribosome-nascent chain complexes followed by proteomic analysis to identify associated factors.