cDNA cloning of rat proteasome subunit RC7‐I, a homologue of yeast PRE1 essential for chymotrypsin‐like activity

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Abstract
The nucleotide sequence of a cDNA that encodes a new subunit, named RC7‐I, of the 20 S proteasome of rat hepatoma cells has been determined. The polypeptide predicted from the open reading frame consists of 201 amino acid residues with a calculated molecular weight of 22,912 and isoelectric point of 7.25. Approximately 80% of the partial amino acid sequences of several fragments of RC7‐I, determined by protein chemical analyses, were found to be in excellent accordance with those deduced from the cDNA sequence. Computer analysis showed that RC7‐I belongs to the β‐type subgroup of proteasomes with similarity to the β‐subunit of the archaebacterial proteasome, differing clearly from α‐type subunits of the proteasome gene family. The overall structure of RC7‐I was found to be homologous to that of yeast PRE1, which is necessary for chymotryptic activity.