Saitta B, Wang Y M, Renkart L, Zhang R Z, Pan T C, Timpl R, Chu M L
Department of Biochemistry and Molecular Biology, Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
Genomics. 1991 Sep;11(1):145-53. doi: 10.1016/0888-7543(91)90111-q.
The alpha 1(VI) and alpha 2(VI) chains, two of the three constituent chains of type VI collagen, are highly similar in size and domain structure. They are encoded by single-copy genes residing in close proximity on human chromosome 21. To study the evolution of the type VI collagen genes, we have isolated and characterized genomic clones coding for the triple-helical domains of the human alpha 1(VI) and alpha 2(VI) chains, which consist of 336 and 335 amino acid residues, respectively. Nucleotide sequencing indicates that, in both genes, the exons are multiples of 9 bp in length (including 27, 36, 45, 54, 63, and 90 bp) except for those encoding for regions with triple-helical interruptions. In addition, the introns are positioned between complete codons. The most predominant exon size is 63 bp, instead of 54 bp as seen in the fibrillar collagen genes. Of particular interest is the finding that the exon structures of the alpha 1(VI) and alpha 2(VI) genes are almost identical. A significant deviation is that a segment of 30 amino acid residues is encoded by two exons of 54 and 36 bp in the alpha 1(VI) gene, but by a single exon of 90 bp in the alpha 2(VI) gene. The exon arrangement therefore provides further evidence that the two genes have evolved from tandem gene duplication. Furthermore, comparison with the previously reported gene structure of the chick alpha 2(VI) chain indicates that the exon structure for the triple-helical domain of the alpha 2(VI) collagen is strictly conserved between human and chicken.
α1(VI)链和α2(VI)链是VI型胶原蛋白三条组成链中的两条，它们在大小和结构域结构上高度相似。它们由位于人类21号染色体上紧密相邻的单拷贝基因编码。为了研究VI型胶原蛋白基因的进化，我们分离并鉴定了编码人类α1(VI)链和α2(VI)链三螺旋结构域的基因组克隆，这两条链分别由336和335个氨基酸残基组成。核苷酸测序表明，在这两个基因中，外显子的长度均为9 bp的倍数（包括27、36、45、54、63和90 bp），但编码三螺旋中断区域的外显子除外。此外，内含子位于完整密码子之间。最主要的外显子大小为63 bp，而不是在纤维状胶原蛋白基因中看到的54 bp。特别有趣的是，α1(VI)基因和α2(VI)基因的外显子结构几乎相同。一个显著的差异是，α1(VI)基因中一段30个氨基酸残基由两个分别为54 bp和36 bp的外显子编码，而在α2(VI)基因中由一个90 bp的外显子编码。因此，外显子排列进一步证明这两个基因是由串联基因复制进化而来的。此外，与先前报道的鸡α2(VI)链的基因结构比较表明，α2(VI)胶原蛋白三螺旋结构域的外显子结构在人和鸡之间严格保守。
