Taubman M B, Grant J W, Nadal-Ginard B
J Cell Biol. 1987 Jun;104(6):1505-13. doi: 10.1083/jcb.104.6.1505.
The 20-kD regulatory light chain (RLC) plays a central role in the regulation of smooth muscle contraction. Little is known about the structure or expression of smooth muscle myosin light chain (MLC) genes. A cDNA library was constructed in the expression vector, lambda gt-11, with mRNA derived from cultured rat aortic smooth muscle cells. Using antibody generated against tracheal smooth muscle myosin, three cDNA clones encoding a RLC were isolated, one of which, SmRLC-2, represents a full-length transcript of the RLC mRNA. The derived amino acid sequence shows 94.2% homology with the chicken gizzard RLC, and 70 and 52% homology with the rat skeletal and cardiac muscle MLC-2 proteins, respectively. Thus, the gene encoding the putative smooth muscle RLC appears to have originated by duplication of the same ancestor that gave rise to the sarcomeric MLC-2 genes. Contrary to the stringent tissue-specific expression of sarcomeric MLC-2 genes, RNA blot hybridization and S1 nuclease mapping demonstrates that the putative smooth muscle RLC gene is expressed in smooth, sarcomeric, and nonmuscle tissues at significant levels. Primer extension analysis suggests that the same promoter region is used in these different tissues. Thus the putative smooth muscle RLC gene appears to be a gene that is constitutively expressed in a large variety of cells and has a differentiated function in smooth muscle.
20-kD调节性轻链（RLC）在平滑肌收缩调节中起核心作用。关于平滑肌肌球蛋白轻链（MLC）基因的结构或表达所知甚少。用培养的大鼠主动脉平滑肌细胞的mRNA在表达载体λgt-11中构建了一个cDNA文库。利用针对气管平滑肌肌球蛋白产生的抗体，分离出三个编码RLC的cDNA克隆，其中一个SmRLC-2代表RLC mRNA的全长转录本。推导的氨基酸序列与鸡肫RLC有94.2%的同源性，与大鼠骨骼肌和心肌MLC-2蛋白分别有70%和52%的同源性。因此，编码假定的平滑肌RLC的基因似乎起源于产生肌节MLC-2基因的同一祖先的复制。与肌节MLC-2基因严格的组织特异性表达相反，RNA印迹杂交和S1核酸酶作图表明，假定的平滑肌RLC基因在平滑肌、肌节和非肌肉组织中均有显著水平的表达。引物延伸分析表明，这些不同组织中使用的是相同的启动子区域。因此，假定的平滑肌RLC基因似乎是一个在多种细胞中组成性表达且在平滑肌中具有分化功能的基因。
