Extensive polymorphism surrounding the murine Ia Aβ chain gene

A segment of the murine immune response-associated (Ia) antigen Aβ chain mRNA has been cloned, and this cDNA clone has been used to examine the organization of the genes encoding these highly polymorphic cell surface proteins. To isolate this clone, pIAβ-1, the authors screened 5000 cDNA clones by a filter hybridization-selection assay using a rabbit heteroantiserum to identify the Aβ chain produced in in vitro translation reactions. This clone corresponds to a segment of the mRNA encoding the β chain of the murine I-A antigen. The 464 bp nucleotide sequence of the insert is consistent with a cDNA clone encoding the carboxyl end of the murine Aβ chain. Comparison of this nucleotide sequence to a human Iaβ chain-derived cDNA clone suggests that the two clones could encode proteins that are about 90% homologous in this region. Southern blot analysis using pIAβ-1 as a probe to investigate the structure of the Aβ chain gene in inbred strains of mice allows two conclusions. First, there is only one Aβ chain gene homologous to this cDNA clone in each haploid mouse genome. Second, the restriction fragments encoding this gene are highly polymorphic. The authors postulate that the mechanism which generates polymorphic variation of the Aβ chain may be involved in generating the restriction site polymorphism within or near the Aβ chain gene.