Subdivision of the S region of the mouse major histocompatibility complex by identification of genomic polymorphisms of the class III genes.

The S region of the mouse major histocompatibility complex (MHC) encodes the class III proteins, the second (C2) and fourth (C4) components of complement, and factor B. Previously, the assignment of S-region haplotypes was based on analysis of protein polymorphisms. The recent availability of C2, C4, and factor B cDNA probes prompted a search for restriction fragment length polymorphisms which would serve as additional genetic markers for these loci. DNA was isolated from livers of mice of all standard inbred H-2 haplotypes and of haplotypes pz and bs. These DNA samples were digested with restriction endonucleases and analyzed by Southern blot. By the pattern of restriction fragment length polymorphism observed, specific markers have been identified in factor B of haplotypes f, u, z, bs, r, and v, and in C4 of haplotypes b,q,f,j,p,s,pz,r, and v. These genetic markers were used in the analysis of S-region composition in strains B10.TFR5(H-2ap5) and C3H.LG(H-2dx), and a possible intra-S-region recombinant was revealed in the H-2dx haplotype. The genetic markers identified here subdivide the S region and will be of value in defining further the composition of the complement gene complex of the mouse MHC.