cDNA cloning of p40, a regulatory subunit of the human 26S proteasome, and a homolog of the Mov-34 gene product.

The nucleotide sequence of a cDNA that encodes a new regulatory subunit, named p40, of the 26S proteasome of human hepatoblastoma HepG2 cells has been determined. The polypeptide predicted from the open reading frame consists of 324 amino acid residues with a calculated molecular mass of 37020 and isoelectric point of 6.03. A KEKE motif, consisting of a very hydrophilic domain rich in 'alternating' lysine (positive) and glutamate (negative) residues, is present in the C-terminus of p40. The overall structure of p40 is homologous to that of the mouse Mov-34 gene product, whose gene disruption by proviral integration results in a recessive embryonic lethality. Thus the p40/Mov-34 protein is a novel essential regulatory subunit of the human 26S proteasome.