Tissue Specific Function of Basement Membrane and Heterogeneity in Matrix Molecules

我们分离了编码人和兔α 4（IV）胶原蛋白链的重叠cDNA。克隆的表征和测序证明了人和兔α 4（IV）胶原蛋白链的一级结构。该链的氨基酸序列与α 2（IV）胶原蛋白链的氨基酸序列同源。原位杂交结果表明该基因位于染色体2 q35 -37.1。有趣的是，编码α 4（IV）胶原蛋白链的mRNA的大小显著大于IV型胶原蛋白链的其他四种mRNA。对这五条α（IV）链的序列进行比较，发现该基因有两个亚类：α 1、α 3和α 5链的基因以及α 2和α 4链的基因。通过这些分析，我们预测还有一条α（IV）链属于α 2（IV）和α 4（IV）链的基因。使用低严格条件下，我们成功地分离出一种新的cDNA编码又一个α（IV）胶原蛋白链。我们将他的新链命名为α 6（IV）链。感兴趣的是，该基因的染色体位置被分配到染色体Xq 22，这是与α 5（IV）胶原蛋白链基因相同的位置。我们进一步分离了同时编码α 6（IV）链和α 5（IV）链的基因的几个片段。对基因片段的精确分析表明，这些基因位于同一片段上，但方向相反，在基因的中心共有双向启动子。此外，在α 6（IV）基因的真实启动子下游约1000个碱基处存在替代启动子。

We isolated overlapping cDNAs encoding the human and rabbit alpha4(IV) collagen chains. Charcterization and sequencing of the clones demonstrated the primary structure of the human and rabbit alpha4(IV) collagen chains. The amino acid sequence of the chain is homologous to that of the alpha2(IV) collagen chain. Chromosomal location of the gene was assigned to chromosome 2q35-37.1 by in situ hybridization. Interestingly, the size of the mRNA coding for the alpha4(IV) collagen chain is significantly larger than the other four mRNAs for type IV collagen chains. Comparison of the sequences for these five alpha(IV) chains revealed that there are two subclasses of the gene ; the genes for alpha1, alpha3, and alpha5 chains and genes for alpha2 and alpha4 chains. By these analyzes we predicted that there was one more alpha(IV) chain that belonged to the genes for the alpha2(IV) and alpha4(IV) chains. Using low stringency conditions we successfully isolated a novel cDNA encoding yet another alpha(IV) collagen chain. We designated his new chain as alpha6(IV) chain. Of interest was that the chromosomal location of the gene was assigned to chromosome Xq22, which is the same location as the gene for alpha5(IV) collagen chain. We furtheer isolated several fragments of the gene coding for the alpha6(IV) chain and also the alpha5(IV) chain at the same time. Precise analysis of the fragment of the genes revealed that the genes were located on the same fragement but aligned onto the opposite directions sharing bidirectional promoter in the center of the genes. Further, there was an alternativepromoter approximately 1000 bases downstream of the authentic promoter for the alpha6(IV) gene.