Genes for C4b-binding protein ?- and ?-chains (C4BPA andC4BPB) are located on chromosome 1, band 1q32, in humans and on chromosome 13 in rats

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Abstract
C4b-binding protein is involved in the regulation of the complement system. It is a multimeric protein composed of seven identical α-chains and a single copy of a unique β-chain. The latter was identified only recently and its structure determined by cDNA cloning. Both subunits in C4b-binding protein belong to the same superfamily of proteins composed predominantly of tandemly arranged short consensus repeats (SCR) approximately 60 amino acid residues in length. The gene for the human α-chain is known to be located in a gene cluster on chromosome 1, band 1q32, which is called the regulators of complement activation (RCA) gene cluster. We have used cDNA probes for both α- and β-chains of human C4b-binding protein to localize their genes with an in situ hybridization technique. We find the genes for both chains to be located on chromosome 1, band 1q32, in the human. This suggests that the β-chain gene is also a member of the RCA gene cluster and that the α- and β-chain genes are located close to each other. The cDNA probes for the α- and β-chains also were used to screen mouse-rat somatic cell hybrids using Southern blotting to localize their genes in the rat. Both the α- and β-chain genes were shown to be located on chromosome 13 in the rat. These are the second and third genes to be located on rat chromosome 13, and the results suggest that the genes for the α- and the β-chains together with the gene for coagulation factor V represent a conserved chromosomal region in rat and man.