Molecular genetics of the S region of the murine H-2 major histocompatibility complex.

The mouse H-2S region has been conventionally identified by the functional, serological and electrophoretic variations of two plasma proteins which constitute its primary genetic markers, C4 (the fourth component of complement) and C4-Slp (sex-limited protein). Recently, recombinant DNA procedures applied in our laboratory as well as in several others have made available molecular clones corresponding to these two nonallelic genes. This paper focuses on the progress provided by the study of C4 and C4-Slp cDNA and genomic clones, as well as by the application of such clones to the probing of the S region structure in conventional and special H-2 haplotypes. At variance with the K, I and D regions of H-2, the S region contains genes which have no obvious structural interrelationship, although in some cases they display a functional interaction. The heterogeneity of S region products is emphasized by the recent detection of steroid 21-hydroxylase genes associated with each of the C4 gene copies.