Molecular basis of genetic polymorphism in major histocompatibility complex-linked proteasome gene (Lmp-2)

Four genes, closely linked to major histocompatibility complex (MHC) class II genes, have been identified in humans, mice, and rats and are thought to be involved in the generation and transport of endogenous immunogenic peptides for the MHC class I antigen-processing pathway. The Tap-1 and Tap-2 genes presumably encode a heterodimeric protein complex responsible for transporting endogenous immunogenic peptides to the lumen of the endoplasmic reticulum. The Lmp-2 and Lmp-7 gene products are two subunits of the large cytosolic proteasome complex possibly involved in generation of endogenous peptides. To study the genetic polymorphism of the Lmp-2 gene, we used a published cDNA sequence as a consensus sequence and PCR-amplified, cloned, and sequenced the Lmp-2 gene from 12 inbred mouse strains. We found three amino acid variants, LMP-2^d, LMP-2^b, and LMP-2^q, which partially correlated with restriction fragment length polymor-phism variants identified with Southern blots. Allelic polymorphism of the Lmp-2 gene may be involved in peptide selection, leading to autoimmune disease susceptibility.