Molecular cloning of cDNAs for two subunits of rat multicatalytic proteinase. Existence of N-terminal conserved and C-terminal diverged sequences among subunits.

cDNA clones for two subunits (designated subunits K and L) of rat liver multicatalytic proteinase (MCP) were isolated using oligonucleotide probes synthesized according to their partial amino acid sequences. The encoded polypeptides of subunits K and L consisted of 255 and 261 amino acid residues with calculated molecular mass of 28.3 kDa and 29.5 kDa, respectively. Northern blot analysis revealed that subunits K and L were expressed in all tissues examined and their expression patterns were almost identical. The deduced amino acid sequences showed no similarities to known protein sequences other than the recently reported sequences of rat and Drosophila MCP subunits. Sequence comparison of MCP subunits of rat and Drosophila revealed that the N-terminal two-thirds of the sequence (especially the N-terminal approximately 20 residues) is conserved, but the C-terminal third of the sequence shows no similarity, suggesting functional and structural roles for both regions. Implications for the structural and functional aspects of MCP subunits are discussed based on the sequence similarity.