PHYSICAL MAPPING OF THE E C AND GRC REGIONS OF THE RAT MAJOR HISTOCOMPATIBILITY COMPLEX/

Alignment of class I-hybridizing cosmids from an R21 (A(l)B(l)D(l)E(u) grc(+)) genomic DNA library gave two contigs: one [150 kilobases (kb)] encompassed the E/C region, or a large part thereof, and the other (1 10 kb) contained the grc region which has genes influencing resistance to chemical carcinogens (vee), fertility (ft), and growth (dw-3). Amp lification of gene sequences in the four cosmids in the E/C region usi ng E(u)-specific and LW2 (RT1.C)-specific primers showed that each cos mid contained both E(u)-like and C-like genes. They are clearly differ ent but closely associated, and they show some variation from the prot otypic E (E(u)) and C (LW2) genes, respectively. Comparison of DNA fro m grc(+) and grc(-) strains of rats showed that the deletion in the gr c(-) strains was approximately 50 kb, and that it was located on two o f the three cosmids in the grc-region contig. The use of specific clas s I probes showed that the grc region contained tandemly duplicated RT 1.O-RT1.N genes and that the RT.BM1 loci lay outside of the grc region . Neither contig reacted with probes specific for class II, TNFA, Hsp7 0, or RT1.M genes. The data presented here and the previous data in th e literature (summarized in Gill et al. 1995) suggest that the gene or der in the major histocompatibility complex (MHC) and MHC-linked regio n of the rat is: A-E/C-grc-M.