Structure of the amino-terminal portion of the murine alpha 1(IV) collagen chain and the corresponding region of the gene.

Collagen IV, the major structural component of basement membranes, is composed of two genetically distinct polypeptide chains, alpha 1(IV) and alpha 2(IV). We have isolated a 522-base-pair (bp) cDNA to the 5' portion of the murine alpha 1(IV) chain mRNA from a library constructed by specific primer extension of poly(A)+ RNA from differentiated F9 cells. This cDNA includes 141 bp of 5' untranslated sequence and encodes a signal peptide plus a portion of the amino-terminal cross-linking (7 S) domain. This cDNA clone was used to obtain the 5' portion of the murine alpha 1(IV) gene from which the nucleotide sequence of exons 1-6 was determined. Exon 1 (234 bp) codes for the 5' untranslated sequence, and the first 28 residues of the protein. The 5' untranslated sequence is highly conserved between the mouse and human species and has the potential to form three mutually exclusive stem-loop structures which may play a role in post-transcriptional regulation. Exons 2-6, which code for the 7 S domain, were found to be 60, 90, 45, and 63 bp in size. The exon structure for the helical portion of the 7 S domain is different from that of the major helical domain, suggesting that they evolved differently.