Complete primary structure of the human type IV collagen alpha 4(IV) chain. Comparison with structure and expression of the other alpha (IV) chains.

The entire sequence of the human alpha 4(IV) collagen chain was determined from cDNA clones and polymerase chain reaction-amplified DNAs. The complete translation product has 1,690 amino acid residues and the processed alpha 4(IV) chain proper 1,652 residues. There is a 38-residue putative signal peptide, a 1,421-residue collagenous domain starting with a 23-residue noncollagenous sequence, and a 231-residue NC1 domain. The Gly-Xaa-Yaa-repeat sequence of the collagenous domain is interrupted at 26 locations by noncollagenous sequences of 1-12 residues in length. The alpha 4(IV) chain contains 31 cysteine residues of which 18 are conserved in the other type IV collagen alpha chains. The calculated molecular weight of the mature alpha 4(IV) chain is 164,123. Analysis of the primary structure showed that the alpha 4(IV) chain belongs to the alpha 2-like type IV collagen chains together with alpha 2(IV) and alpha 6(IV). Northern analyses with RNA from several human fetal tissues revealed quite similar expression patterns for the alpha 4(IV) and alpha 3(IV) chains, but there were also distinct differences in some tissues. The expression patterns of alpha 5(IV) and alpha 6(IV) differed extensively between each other and they also differed from those of alpha 3(IV) and alpha 4(IV).