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 RT1k haplotypes 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 RT1u haplotypes differed by less than 6%. However, intra-RT1a, intra-RT1b, and intra-RT1l restriction fragment differences were between 50 and 64%. In specific cases, different RT1 haplotypes associated with identical class I restriction patterns, e.g., RT1m (MNR) and RT1d (MR); higher resolution confirmed the difference (two bands) between RT1m and RT1d. Results of hybridization with the human DC1 beta probe confirmed that the AVN RT1a and NSD RT1b haplotypes 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.