CHARACTERIZATION OF A CLASS-IB GENE OF THE RAT MAJOR HISTOCOMPATIBILITY COMPLEX

The cDNA and a partial genomic sequence of a rat class I major histoco mpatibility (RT1) gene, 11/3R, is reported here. The sequence contains several unique amino acid residues at certain positions, mutations in exon 7 (which is not expressed), a mutation of the canonical exon 8 s top codon to a sense codon, and includes a long 3' untranslated region (utr). The structure of exon 7 differs from that found in most rat cl ass I genes and resembles exon 7 of most H-2K,D,L,Q genes. Parts of th e 3' noncoding region are homologous to the RT1.A-4 and certain H-2 ge nes. Expression is detectable by northern blot analysis in mitogen-sti mulated lymphocytes only, by polymerase chain reaction (PCR) in each t issue tested. After transfection into L cells 11/3R can be shown to be expressible at the cell surface. Probes derived from the 3' noncoding part crosshybridize with a number of restriction fragments which map to the RT1.C region, thus defining a subfamily of RT1.C region genes. Several members of this subfamily are deleted in the lm1 RT1 mutant. T he 11/3R gene presents typical features of a class lb gene. Aspects of evolution and the potential function of the gene are discussed.