Studies on murine Ss protein: demonstration that S region encodes structural gene for fourth component of complement

Although genes controlling the expression of certain complement components have been shown to be linked to the major histocompatibility complex of several species, the structural genes that encode these molecules have been more difficult to map. In this study, the three constitutive polypeptide chains of the fourth component of murine complement (C4) (alpha, beta, and gamma) were isolated from 14 different inbred strains and compared by peptide mapping on analytical sodium dodecyl sulfate gels. The peptide patterns of the alpha and gamma subunits appeared to be nearly identical, but two distinctly different patterns were observed for the C4 beta chain. This structural variant was mapped to the S or G region and, as such, provides direct evidence that a structural gene for a complement component is encoded within a major histocompatibility complex.