Complete nucleotide and derived amino acid sequences of the fourth component of mouse complement (C4). Evolutionary aspects.

The nucleotide sequence coding for the fourth component of mouse complement (C4) has been determined from a cloned genomic DNA fragment and a cloned cDNA fragment. The amino acid sequence of the protein was deduced. The single chain precursor protein (pro-C4) consists of 1719 amino acid residues. The mature beta, alpha, and gamma subunits contain 654, 766, and 291 amino acids, respectively. One potential carbohydrate attachment site is predicted for the beta chain, three for the alpha chain, and none for the gamma chain. From a comparison with human C4 cDNA sequence an extensive overall sequence homology, 79% in nucleotides and 76% in amino acids, is observed. There is conservation in both the position and number of cysteine residues in human and mouse C4. We compared the mouse C4 amino acid sequences with those of mouse C3 and human alpha 2-macroglobulin and the evolutionary relationship among these three proteins is discussed.