Class I and class II restriction pattern polymorphisms associated with independently derived RT1 haplotypes in inbred rats

This communication reports the DNA level identification of class I and class II sequences associated with 20 RT1 haplotypes which have been assigned previously to eight RT1 groups. Sixteen to 22 bands in genomic blots hybridized with the mouse pH-2III class I cDNA probe. Only the three RT1^khaplotypes associated with identical class I restriction fragment patterns. Differences in restriction bands between putatively identical RT1 haplotypes were either less than or equal to 6%, or greater than 50%, suggesting a relatively high level of recombination between serologically identified RT1.A genes and the majority of class I sequences. Restriction fragment patterns associated with three RT1^uhaplotypes differed by less than 6%. However, intra-RT1^a,intra-RT1^b,and intra-RT1^lrestriction fragment differences were between 50 and 64%. In specific cases, different RT1 haplotypes associated with identical class I restriction patterns, e.g., RT1^m(MNR) and RT1^d(MR); higher resolution confirmed the difference (two bands) between RT1^mand RT1^d.Results of hybridization with the human DC_{1 β}probe confirmed that the AVN RT1^aand NSD RT1^bhaplotypes were generated by recombinations within the vicinity of the RT1.B : RT1.D regions. These results demonstrate that a previous classification of RT1 haplotypes was incomplete and did not include the majority of class I and class II sequences which distinguish RT1 haplotypes.