Major histocompatibility-encoded human proteasome LMP2. Genomic organization and a new form of mRNA

LMP2 is one of the two proteasome subunits encoded by genes in the major histocompatibility complex class II region. Here we report the genomic organization of human LMP2 gene. Sequence analysis of polymerase chain reaction-amplified cDNA from a number of lymphoblastoid cell lines demonstrated two forms of LMP2 mRNA, one (LMP2.1) complete and homologous to the published LMP2 genomic sequence from cosmid clones, and the other (LMP2.s) a smaller transcript resulting from splicing of a 30-base pair fragment from the first exon. Antibodies to recombinant LMP2.s protein (22.3 kDa) were raised in rabbits. This anti-LMP2.s serum recognized both recombinant proteins (LMP2.1 = 23.3 kDa and LMP2.s = 22.3 kDa) and a single protein of 21.5 kDa molecular mass in lysates from human lymphoblastoid cell lines. Pulse-chase experiments demonstrated that LMP2 polypeptide also undergoes processing from 22.3- to 21.5-kDa protein when incorporated into proteasomes. These data suggest that the processing of human LMP2 subunit takes place both at the transcription and post-translational levels. Northern blot analysis showed that the LMP2 mRNA is expressed in lymphoblastoid cell lines and in fibroblasts following gamma-interferon induction, but not in brain, smooth muscle, fibroblasts (uninduced), and colon epithelial cells.