Molecular analyses of genes in the rabbit MHC (RLA) by pulsed field gel electrophoresis have shown that the relative order of class II genes (DP, DO, DQ, DR) is identical to that in humans and similar to that in the mouse. However, a major difference from either HLA or H-2 was observed at the DR end of the RLA class II complex: class I genes are located in close proximity to DR with no interposed class III sequences. A MluI fragment of 180 kb and a 210-kb SalI fragment both hybridized with the

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... R probe as well as with different class I probes including that for pR27, a class I gene with T cell-limited pattern of expression. Comparison of two different RLA haplotypes, A and B, indicated that the distance between the DQ and DR subregions differs by approximately 700 kb in the two haplotypes. Testing other unrelated rabbits suggested that this difference segregates within the rabbit population and presumably derives from an insertion/deletion event in different haplotypes. A further difference between the A and B haplotypes included variable distance between genes encoding DO beta and DP; the DR end of the complex and the class I genes linkage was conserved in the two haplotypes.