Further biochemical data on Qa-2.

The Qa-2 differentiation alloantigen is coded by a gene situated between the D and Tla loci of the murine major histocompatibility complex (H-2). Qa-2-bearing protein was isolated by immunoprecipitation and found to be composed of subunits of 40 000 and 12 000 daltons by SDS polyacrylamide gel electrophoresis (PAGE). The 12 000 dalton material was identified as beta 2-microglobulin (beta 2M) by its molecular weight (SDS PAGE), charge (isoelectric focusing), antigenicity (reactivity with xenogenic anti-beta 2M), and genetics. The 40 000 dalton mol. wt. of Qa-2 heavy chains is 5 000 daltons less than that of D and K molecules (45 000 daltons). The quantity of Qa-2 isolated by immunoprecipitation was found to vary in strain-specific fashion and as much as a 15-fold difference was observed.