A mutant rat major histocompatibility haplotype showing a large deletion of class I sequences.

The LEW. 1LM1 inbred rat strain, which has been derived from a (LEW x LEW.1W) F2 hybrid, carries a major histocompatibility (RT1) haplotype which is distinct from that of the LEW strain (RT1(1)) in that certain RT1.C region-determined class I antigens are not expressed. Here we show that this phenotypic defect is due to genomic deletion of about 100 kb of the RT1.C region. Certain deleted DNA fragments have been cloned from the wild-type DNA into the EMBL4 vector. Five clones have been characterized and are shown to possess different restriction maps and to each carry a single stretch of class I cross-hybridizing sequences. Probes derived from the non-class I coding part of two clones detect fragments which are present in the wild-type but absent from the lm1 mutant. The type of deletion described here in the rat is discussed in the context of H-2D/Q deletions in the mouse.