Restricted homology between human alpha 1 type IV and other procollagen chains.

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Abstract
Screening of a human fibroblast c[complementary]DNA library with a mouse type IV procollagen clone resulted in one 1.05-kilobase isolate that was used to identify a 1.7-kilobase clone overlapping the former by < 150 nucleotides, EcoRII digestion revealed that the larger clone exhibited the pattern characteristic of DNA coding for a collagenous sequence. Blot hybridization to RNA from mouse F9 stem cells and from these cells treated with retinoic acid and N6,O2''-dibutyryl-cAMP showed induction of type IV mRNA. DNA sequencing and comparison of the derived amino acids with the reported protein data demonstrated that the clones encode part of the .alpha.1 chain of human type IV procollagen. Alignment of .alpha.1(IV) with other human procollagens showed minimal but detectable homology. A small cluster of charged residues in the .alpha. chain is partially shared by type IV. In close proximity is an interruption in the .alpha.1(IV) Gly-Xaa-Yaa region corresponding to the 3'' end of a unique proline-free, and therefore also less rigid, area in other collagen triple helices. Analysis of the carboxyl-terminal .alpha.1(IV) peptide showed a repeat symmetry possibly dictated by the 6 cysteines in each half of the structure. The position of 5 cysteines in addition to 4 tyrosine/tryptophan groups allowed a correlation to be drawn between the 3'' noncollagenous type IV region and the larger, highly conserved carboxyl propeptides of other human procollagens. Such similarities in the different chains may define functional domains conserved throughout evolution.