cDNA isolation and partial gene structure of the human α4(IV) collagen chain

A novel collagen IV chain, α4(IV), has recently been identified in basement membranes. We describe part of the primary structure of the human α4(IV) polypeptide for the first time, which has been determined by cloning and sequencing of cDNAs encoding 241 amino acid residues of the COL domain and 231 residues of the NC1 domain. We also characterized a genomic DNA fragment containing 4 exons coding for the entire NCl domain. Among five known α chains of collagen IV, the α4(IV) chain is distinct from the other four chains. However, it is more similar to the α2 (IV) chain than to the α1(IV), α3(IV) and α5(IV) chains in terms of amino acid sequence homology, domain structure of polypeptides and exon/intron structure of the genes, suggesting the presence of two phylogenetically distinct subclasses of collagen IV α chains; one composed of α2 and α4 chains and the other of α1, α3 and α5 chains.