Class II genes of miniature swine. I. Class II gene characterization by RFLP and by isolation from a genomic library.

Class II genes of miniature swine have been characterized by restriction fragment length polymorphism (RFLP) analysis and by analysis of a series of clones isolated from a lymphocyte genomic library. For RFLP analysis, DNA samples from three independent major histocompatibility complex homozygous lines and three intra-MHC recombinant lines were digested with a variety of restriction enzymes and analyzed in Southern blots using human cDNA probes for DP, DQ, DR, and DZ alpha genes, and DP, DQ, DR, and DO beta genes. One, or at most two, unique fragments were detected by hybridization with each of the human alpha probes tested. In contrast, multiple bands (five to six for most enzymes examined) were detected by each of the human beta probes tested, the majority of which were found to cross-react with at least three of these probes under conditions of moderate stringency. Genomic DNA from the SLAc haplotype was cloned into an EMBL-3 bacteriophage vector, and the corresponding genomic library was screened with each of these human cDNA probes. The class II genes thereby isolated from this library showed characteristics consistent with those anticipated from the RFLP analysis. Thus, unique alpha genes were obtained which showed no evidence of cross-hybridization, while beta genes showed extensive cross-hybridization and were frequently detected in the library by more than one human beta gene probe. These data are consistent with early evolutionary divergence of alpha genes, prior to mammalian speciation, and with continuing evolution of beta genes, with possible shared usage of these genes by different alpha loci. The data also imply that alpha genes can readily be assigned to loci homologous to their human counterparts, but that beta genes will require further mapping and/or sequence analysis to confirm assignments.