Binds specifically to cytosolic chaperonin (c-CPN) and transfers target proteins to it. Binds to nascent polypeptide chain and promotes folding in an environment in which there are many competing pathways for nonnative proteins. Represses the transcriptional activity of MYC. . This is the function of Ensembl gene identifier ENSG00000123349 (PFDN5, prefoldin subunit 5).