cDNA cloning and sequencing of component C8 of proteasomes from rat hepatoma cells

The primary structure of component C8 of rat proteasomes (multicatalytic proteinase complexes) has been determined by sequencing on isolated cDNA clone. C8 consists of 255 amino acid residues with a calculated molecular weight of 28,417. These values are consistent with those obtained by protein chemical analyses. Computer-assisted homology comparison showed that C8 is a new protein, differing from all proteins reported so far. The overall amino acid sequence of C8 resembles those of most other components of proteasomes reported, such as components C2, C3 and C9 of rat proteasomes and certain components of other eukaryotic proteasomes, such as those of Drosophila and yeast, but shows little similarity with component C5 of rat proteasomes. C8 showed particularly close structural similarity to component YC1 of yeast proteasomes, suggesting that C8 has been highly conserved during evolution and functions ubiquitously in all eukaryotes.