Two human cDNA libraries prepared from normal fibroblast (GM3348) and rhabdomyosarcoma (CCL136) mRNAs were screened under cross hybridization conditions with a genomic fragment coding for exons 2 and 3 of the avian type III procollagen COOH-propeptide (Yamada, Y., Mudryj, M., Sullivan, M. and deCrombrugghe, B. (1983) J. Biol. Chem. 258, 2758-2761). One cDNA clone containing a 1.12 kb insert was isolated from the CCL136 library and later used to identify a GM3348 derived clone with a 2.4 kb insert. Comparison of the human and avian type III C-terminal propeptides revealed much more divergence in the first 54 amino acids following the terminal cysteine of the triple helical region than is present in the alpha 1(I) and alpha 2(I) procollagen chains of these species. Analysis of poly (A+) RNA from normal human fibroblast and tumor cell lines showed that they differed greatly in the relative amounts of alpha 1(I), alpha 2(I), and alpha 1(III) mRNAs. Furthermore, as we previously reported for the alpha 1(I) and alpha 2(I) transcripts, multiple mRNAs also hybridize to the cloned alpha 1(III) DNA.

Screening of a human fibroblast cDNA library with a mouse type IV procollagen done resulted in one 1.05-kilobase isolate that was used to identify a 1.7-kilobase clone overlapping the former by <150 nucleotides. EcoRl 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 N',02'-dibutyryl-cAMP

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