[Cloning of cDNA for C3, the third component of complement (author's transl)]

A collection of bacterial plasmids has been constructed carrying cDNA inserts corresponding to mouse liver C3. Eight overlapping cDNA fragments cover 4 700 out of the 5,100 +/- 200 nucleotides of the mRNA including its 3'-end. By partial DNA sequencing it has been found that the beta-chain is encoded in the 5'-half of the mRNA and must thus be located in the amino-terminal portion of the precursor polypeptide pro C3. From DNA sequences it is predicted that the amino-terminus of mouse C3-beta coincides in 12/15 residues with the known amino-acid sequence of guinea-pig C3 beta and in 9/10 residues with that of human C3 beta. A gene bank has been constructed from mouse DNA, from which four C3 genomic clones have been isolated. Two of them carry direct neighbouring fragments of 14- and 18-kilobase pairs of DNA, and contain one entire C3 gene (24-kilobase pairs). The 3'- and 5'-ends of the gene have been mapped. The DNA sequence at the 5'-end predicts that the initial translation product of the C3-mRNA is a prepro C3 molecule which carries at its amino-terminus a signal peptide of 24 amino-acids of typical composition. Human C3 genomic clones have been isolated and used to map the human C3 gene on a chromosome.