UniProtKB description: Component of the ribosome, a large ribonucleoprotein complex responsible for the synthesis of proteins in the cell. The small ribosomal subunit (SSU) binds messenger RNAs (mRNAs) and translates the encoded message by selecting cognate aminoacyl-transfer RNA (tRNA) molecules. The large subunit (LSU) contains the ribosomal catalytic site termed the peptidyl transferase center (PTC), which catalyzes the formation of peptide bonds, thereby polymerizing the amino acids delivered by tRNAs into a polypeptide chain. The nascent polypeptides leave the ribosome through a tunnel in the LSU and interact with protein factors that function in enzymatic processing, targeting, and the membrane insertion of nascent chains at the exit of the ribosomal tunnel (PubMed:22096102). Located at the head of the 40S ribosomal subunit in the vicinity of the mRNA exit channel, RACK1 serves as a scaffold protein that can recruit other proteins to the ribosome. Involved in induction of the ribosome quality control (RQC) pathway; a pathway that degrades nascent peptide chains during problematic translation (PubMed:28223409, PubMed:30465652). Involved in the negative regulation of translation of a specific subset of proteins (PubMed:15340087).