The present invention provides polynucleotides which identify and encode novel human proteasome subunit proteins. The invention provides for genetically engineered expression vectors and host cells comprising the nucleic acid sequences encoding PSUB. The invention also provides for the use of substantially purified PSUB, antagonists, and in pharmaceutical compositions for the treatment of diseases associated with the expression of PSUB. Additionally, the invention provides for the use of antisense molecules to PSUB in pharmaceutical compositions for treatment of diseases associated with the expression of PSUB. The invention also describes diagnostic assays which utilize diagnostic compositions comprising the polynucleotide, fragments or the complement thereof, which hybridize with the genomic sequence or the transcript of polynucleotides encoding PSUB or anti-PSUB antibodies which specifically bind to PSUB.