nascent polypeptide-associated complex (NAC)

Function

• prevents inappropriate targeting of non-secretory polypeptides to the endoplasmic reticulum (ER)
• binds to nascent polypeptide chains as they emerge from the ribosome & blocks their interaction with the signal recognition particle (SRP), whic targets nascent secretory peptides to the ER
• diminishes inherent affinity of ribosomes for protein translocation sites in the ER membrane (M sites)
• associates with ribosomes through the BTF3 subunit

Structure

• consists of NACA & BTF3 (both subunits can contact nascent polypeptide chains)

More general terms

• chaperonin; chaperone
• molecular complex