Two mRNAs exist for the Hs PROS-30 gene encoding a component of human prosomes

Screening of a lambda gt11 cDNA expression library of the HeLa cell genome with a monoclonal antibody that specifically recognizes prosomal 30-33-kDa proteins, allowed isolation of a 1264-nucleotide (nt) recombinant cDNA containing a 327-nt untranslated 5'-end. The amino acid (aa) sequence deduced from this cDNA revealed a protein of 269 aa (M(r) of 30,227) that includes a consensus box characteristic for Tyr phosphorylation, also observed in other prosomal proteins. Comparison with another prosomal 27-kDa protein, cloned in our laboratory, indicated the presence of three prosome-specific homology boxes observed in these proteins from archaebacteria to man. Interestingly, except for the untranslated 5'-end, as well as the sequence coding for the N-terminal six aa, this cDNA is identical to two recently published cDNAs encoding subunit C2 of human liver proteasome [Tamura et al., Biochim. Biophys. Acta 1089 (1991) 95-102] and subunit NU of human erythrocyte macropain [DeMartino et al., Biochim. Biophys. Acta 1079 (1991) 29-38]. Primer extension and Northern blot analysis using two specific 18-mer oligodeoxyribonucleotides indicated the presence of two mRNAs that have divergent 5'-ends. These results, as confirmed by the polymerase chain reaction, establish the existence of two distinct Hs PROS-30 mRNAs, differing in their 5'-noncoding regions and in the N-terminal six aa of their protein products.