GENOMIC ORGANIZATION AND TISSUE EXPRESSION OF THE MOUSE PROTEASOME GENE LMP-7

LMP7 is one of the two proteasome subunits encoded in the major histoc ompatibility complex and is speculated to play a role in the generatio n of endogenous peptides for presentation by class I molecules to cyto toxic T cells. Here we report the genomic organization of the mouse Lm p-7 gene and the tissue distribution of its messenger RNA. In contrast to human LMP7 which is composed of seven exons and six introns, the m ouse Lmp-7 gene is organized in six exons and five introns. Interestin gly, the region corresponding to the first exon of human LMP7 is highl y modified by numerous insertions and deletions and contains two in fr ame stop codons. Consequently, the mouse Lmp-7 gene does not allow the alternative exon usage described in humans and most likely encodes fo r only one LMP7 protein. Thus, the Tap-1 3' end gene region and the Lm p-7 initial translation codon are separated by an 1182 nucleotide regi on which contains a TATA-box, a cAMP regulatory element, two SP1 sites , and two G-C-rich regions. Expression of the Lmp-7 messenger RNA was analyzed on different tissues from unstimulated mice. Lmp-7 messenger RNA is expressed in spleen, thymus, lung, liver, heart, and, at a very low level, in kidney but not in brain and testis. The possible role o f Lmp genes in antigen processing is discussed.