The C4 and Slp genes of the complement region of the murine H-2 major histocompatibility complex

Recent analyses, at the protein and DNA levels of structure, of the murine complement component C4 and the closely related sex-limited protein, Slp have led to new insights into the H-2/S region-linked C4 and Slp genes and their products. The primary products are 200000 Da precursors which are cleaved, intracellularly and extracellularly, into the mature α—β—ϒ-subunit molecules of plasma. Precursor order of subunits is β—α—ϒ; a complementary DNA clone spanning the α—ϒ junction has been extensively analysed. The C-terminal of the α-chain is of particular interest because of post-secretion processing which differentiates ‘secreted’ and ‘plasma’ forms of C4, both apparently functional, and because allelic variants of C4 and the Slp protein, which differ substantially in molecular masses, owe their differences principally to different levels of glycosylation of the α-chain. Allelic variations in rate of C4 synthesis (C4-high compared with C4-low) have been analysed in cultures of hepatocytes and macrophages. Three distinct modes of genetic regulation of the expression of the Slp protein have been identified.