Type III collagen is one of the major interstitial collagens and, as such, plays an important role in modulating the structure and function of most tissues. To compare the expression of the type III collagen gene to that of the type I collagen α 1(I) and α2(I) genes, cDNAs encoding the 3’ one-third of the human α1(III) collagen mRNA were obtained by screening a human fetal lung fibroblast cDNA library with a cloned segment of the chicken αl(III) gene. Northern blot analysis of human fetal lung fibroblast RNA demonstrated two αl(III)-specific mRNAs of sizes 6.6 and 5.8 kilobases, sizes clearly different from those of the type I collagen mRNAs. Analyses of populations of dividing and nondividing human lung fibroblasts revealed that, on a per cell basis, the nondividing population contained twice as much αl(III) mRNA than did the dividing population. The same was true for the type I collagen αl(I) and α2(I) mRNA transcripts. Similar results were obtained when αl(III), α1(I), and α2(I) mRNA transcripts were quantified by using dot blot evaluation of total RNA, Northern analysis of total RNA, and dot blot evaluation of cytoplasmic RNA. Thus, despite the fact that the αl(III) collagen gene is located on a chromosome different from the αl(I) and α2(I) genes, the expression of these three collagen chains appears to be coordinately controlled during periods of rapid and slow fibroblast growth.
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