Structure of murine complement component C3. I. Nucleotide sequence of cloned complementary and genomic DNA coding for the beta chain.

The nucleotide sequence coding for the beta chain of murine C3 was determined from cloned cDNA and genomic DNA fragments. Sonicated subfragments were randomly inserted into the bacteriophage M13 and sequenced using the dideoxynucleotide technique. Each nucleotide was sequenced on average six times in these studies. The derived amino acid sequence includes a signal peptide and a tetra-arginine sequence between the beta and alpha subunits in the precursor polypeptide prepro-C3. Together with the accompanying report (Wetsel, R.A., Lundwall, A., Davidson, F., Gibson, T., Tack, B.F., and Fey, G.H. (1984) J. Biol. Chem. 259, 13857-13862), this paper completes the analysis of the coding sequences for the prepro-C3 polypeptide. The derived molecular weight of the unglycosylated beta chain (642 amino acids) is 70,641. The sequences of the first two introns in the murine C3 gene and of the 5'-flanking 106 nucleotides are also reported. The 5'-flanking region contains a TATA consensus sequence in agreement with an earlier report (Wiebauer, K., Domdey, H., Diggelmann, H., and Fey, G.H. (1982) Proc. Natl. Acad. Sci. U. S. A. 79, 7077-7081), presumed to be involving in regulating the expression of the C3 gene. A striking feature of the derived sequence was that only 3 cysteine residues were found, all located in the C-terminal part of the polypeptide chain. No carbohydrate attachment sites were predicted in the beta chain.