Molecular mapping of the HLA-linked complement genes and the RCA linkage group.

Phenotypic genetics have established linkage of the genes encoding proteins involved in the activation of the complement component C3. C2, factor B and C4, three of the structural components of the classical and alternative pathway C3 convertases, are encoded by genes which have been mapped to the class III region of the major histocompatibility complex (MHC) on human chromosome 6. The regulatory proteins factor H, C4BP, CR1, CR2 and DAF, which are involved in the control of C3 convertase activity, are encoded by closely linked genes, termed the regulators of complement activation (RCA) linkage group, that have been mapped to human chromosome 1. cDNA clones for all these proteins have been isolated, and this has made it possible to investigate the organization and structure of the MHC class III genes and the genes in the RCA linkage group. This short review summarizes some of the main features which have emerged from recent cloning work.