CDNA CLONING OF RAT PROTEASOME SUBUNIT RC10-II, ASSUMED TO BE RESPONSIBLE FOR TRYPSIN-LIKE CATALYTIC ACTIVITY

The nucleotide sequence of a cDNA that encodes a new subunit, named RC 10-II, of the 20S proteasome of rat embryonic brain has been determine d. The polypeptide predicted from the open reading frame consists of 2 05 amino acid residues with a calculated molecular weight of 22,965 an d isoelectric point of 6.15. Computer analysis showed that RC10-II bel ongs to the B-type subgroup of proteasomes, differing clearly from alp ha-type subunits of the proteasome gene family. The primary structure of RC10-II was found to contain the partial amino acid sequences of se veral fragments of subunit 13, which has a cysteinyl residue critical for the trypsin-like catalytic activity, as reported by L.R. Dick et a l. [Biochemistry 31, 7347-7355, 1992], suggesting that RC10-II is a pr oteasomal subunit necessary for the expression of tryptic activity.