H-2 linked ss protein is c4 component of complement.

THE major histocompatibility complex in the mouse encompasses several distinct loci, which, with one exception, control the expression of cell surface glycoproteins. The exception is the Ss-S1p traits1. The Ss trait involves regulation of the level of a plasma protein, the Ss protein2. The S region of the H–2 complex, whose marker gene controls the Ss-protein concentration, also regulates the haemolytic complement level3. This has led to the suggestion that the Ss protein is a component of complement3,4. We have isolated the Ss protein and demonstrate here that it is the murine equivalent of C4.