TCP20, A SUBUNIT OF THE EUKARYOTIC TRIC CHAPERONIN FROM HUMANS AND YEAST

Members of the Hsp60 chaperonin family, such as Escherichia coli GroEL /S and the eukaryotic cytosolic chaperonin complex, TRiC (TCP ring com plex), are double toroid complexes capable of assisting the folding of proteins in vitro in an ATP-dependent fashion. TRiC differs from the GroEL chaperonin in that it has a hetero rather than homo-oligomeric s ubunit composition and lacks a GroES-like regulatory cofactor. We have established greater than 57% identity between a protein en coded by t he TCP20 gene from a human cDNA library and the newly identified prote in encoded by the TCP20 gene located on the right arm of chromosome TV of the yeast Saccharomyces cerevisiae. These Tcp20 proteins showed ap proximately 30% identity to Tcp1, a known subunit of TRiC, Gel filtrat ion, followed by Western analysis of purified bovine testis TRiC with a Tcp20-specific antibody, indicated that Tcp20 is a subunit of the he tero-oligomeric TRiC. Gene disruption experiments showed that TCP20, l ike TCP1, is an essential gene in yeast, consistent with the view that TRiC is required for folding of key proteins. The amino acid sequence similarities and the derived evolutionary relationships established t hat the human and yeast Tcp20 proteins represent members of a new fami ly of subunits of TRiC chaperonins.