Molecular Cloning of CDNA for Proteasomes from Rat Liver: Primary Structure of Component C3 with a Possible Tyrosine Phosphorylation Site

Proteasomes are multicatalytic proteinase complexes consisting of multiple components. Previously, we reported the cloning and sequencing of cDNA for the largest component, C2, of rat liver proteasomes [Fujiwara, T., Tanaka, K., Kumatori, A., Shin, S., Yoshimura, T., Ichihara, A., Tokunaga, F., Aruga, R., Iwanaga, S., Kakizuka, A., & Nakanishi, S. (1989) Biochemistry 28, 7332-7340]. In the present study, the nucleotide sequence of another component (C3) of proteasomes has been determined from a recombinant cDNA clone isolated by screening a rat liver cDNA library with synthetic oligodeoxynucleotide probes corresponding to partial amino acid sequences of the protein. The deduced sequence of component C3 consists of 234 amino acid residues with a calculated molecular weight of 25,925. These values are consistent with those obtained by protein chemical analyses. A single mRNA species hybridizing to the C3 cDNA of rat liver was expressed in all rat tissues examined and in a variety of other eukaryotic organisms, its distribution being similar to that of C2 mRNA. The wide distribution of the gene product, possibly C3, suggests that this protein functions similarly in most eukaryotes. C3 is an unmodified protein of a single gene and differs from any other known protein, but its overall amino acid sequence resembles those of other proteasomal components, including C2, suggesting that these components belong to a single family of proteins with the same evolutionary origin.(ABSTRACT TRUNCATED AT 250 WORDS)