Physical mapping of theE/C andgrc 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 (110 kb) contained the grc region which has genes influencing resistance to chemical carcinogens (rcc), fertility (ft), and growth (dw-3). Amplification of gene sequences in the four cosmids in the E/C region using E ^u -specific and LW2 (RT1.C)-specific primers showed that each cosmid contained both E ^u -like and C-like genes. They are clearly different but closely associated, and they show some variation from the prototypic E (E ^u ) and C (LW2) genes, respectively. Comparison of DNA from grc ⁺ and grc ^– strains of rats showed that the deletion in the grc ^– strains was approximately 50 kb, and that it was located on two of the three cosmids in the grc-region contig. The use of specific class I probes showed that the grc region contained tandemly duplicated RT1.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, Hsp70, or RT1.M genes. The data presented here and the previous data in the literature (summarized in Gill et al. 1995) suggest that the gene order in the major histocompatibility complex (MHC) and MHC-linked region of the rat is: A-E/C-grc-M. Received: 6 November 1995 / Revised: 24 January 1996