Genomic analysis of the H-2 complex region associated with mouse t haplotypes.

Naturally occurring t haplotypes suppress recombination over a region of mouse chromosome 17 that includes the H-2 complex. Each of these t haplotypes is associated with a specific set of H-2 alleles and can be placed into one of a limited number of complementation groups. Genetic studies have demonstrated the existence of a basic homology in genomic organization among all t haplotypes. We used an H-2 cDNA probe to investigate, at the molecular level, possible relationships among the H-2 regions of different t haplotypes. We identified a family of t haplotype-specific restriction fragments that carry DNA sequences homologous to the H-2-like genes. Surprisingly, the H-2-defined restriction patterns from all five complete t haplo-types analyzed are highly homologous, even though H-2 gene products expressed are antigenically distinct. These data lead to two major conclusions. First, all t haplotypes were derived from a small number of closely related ancestors. Second, the H-2 complex region associated with each primordial t chromosome has been maintained within at least the five present-day t haplotypes analyzed here. Hence the H-2 complex is an integral component of naturally occurring t haplotypes.