Regulation of type I collagen synthesis. Total proalpha1(I) and proalpha2(I) mRNAs are maintained in a 2: 1 ratio under varying rates of collagen synthesis

Abstract

The type I collagen molecule contains two α1(I) chains and one α2(I) chain. Previous investigations, using embryonic chick calvaria, have indicated that the two chains are synthesized in a 2:1 ratio which is controlled at a pretranslational level, since the cells contain twice as much translatable proα1(I) mRNA as proα2(I) mRNA. The present report describes hybridization analyses of the cellular levels of total cellular RNAs coding for the proα1(I) and proα2(I) chains, using as probes two cloned cDNAs complementary to chick proα1(I) and proα2(I) mRNA, respectively. Total cellular RNA was extracted from embryonic chick calvaria, proα1(I) and proα2(I) RNA sequences were quantified by Northern hybridization using conditions ensuring that hybridization efficiency and specific radioactivity were the same for the two probes. Similar analyses were carried out on RNA extracted from calvaria with different levels of collagen synthesis after culture in the presence or absence of ascorbic acid. The results for all samples analyzed indicate that total cellular proα1(I) and proα2(I) mRNAs are present in a 2:1 ration which is maintained even during variations in collagen synthesis rate. There is no evidence for regulation mediated by different rates of processing of mRNA precursors, although preferential degradation of the proα2(I) gene transcript cannot be excluded. Thus, the synthesis of type I procollagen chains is presumably coordinated by transcriptional control.