Complete primary structure of the human alpha 3(IV) collagen chain. Coexpression of the alpha 3(IV) and alpha 4(IV) collagen chains in human tissues.

We report the entire primary structure of the human alpha 3(IV) collagen chain determined from cDNA clones and polymerase chain reaction-amplified DNAs. The deduced amino acid sequence demonstrates that the complete translation product consists of 1670 amino acid residues and the mature alpha 3(IV) chain contains 1642 residues with a corresponding calculated molecular mass of 161,753. The full-length translated polypeptide has a signal peptide of 28 amino acids, a 1410-residue collagenous domain starting with a 14-residue noncollagenous sequence, and a 232-residue NC1 domain. There are 23 noncollagenous interruptions in the Gly-X-Y repeat sequence of the collagenous domain. The major transcription start site of the alpha 3(IV) chain gene was also determined from genomic DNA by primer extension and S1 nuclease protection assays. Northern analysis revealed coexpression of the alpha 3(IV) and alpha 4(IV) chains in tissues where expression was observed such as in kidney, muscle, and lung.