Mapping and transcriptional properties of RT1 class II region genes.

The class II region of major histocompatibility complex of the rat. Rattus norvegicus (RT1) consists of RT1.B, RT1.D, and RT1.H subregions. The gene order around the H subregion was determined as RT1.A--H beta-H alpha--B by RFLP analysis of naturally occurring intra-RT1 recombinant rats with HLA DP probes. A unique recombinant strain, LEJ, was found to have its recombinational site between H beta and H alpha (RT1.AuH beta uH alpha bBbDb). Northern analysis of class II mRNAs showed that transcripts of RT1.D alpha, RT1.D beta, and RT1.B alpha shared identical sizes among various strains of rats, but RT1.B beta mRNA showed allele-specific size heterogeneities. Northern hybridization with HLA DP alpha probes detected possible RT1.H alpha transcripts. On the other hand, no clear signal of H beta was observed. BDIX whose RT1.B products had not been identified was found to transcribe B alpha and B beta mRNAs.