Hallauer P L, Hastings K E, Baldwin A S, Pearson-White S, Merrifield P A, Emerson C P
J Biol Chem. 1987 Mar 15;262(8):3590-6.
We describe the analysis of two quail cDNA clones representing distinct but closely related alpha-tropomyosin mRNAs. cDNA clone cC101 corresponds to a 1.2-kilobase RNA which accumulates to high levels during myoblast differentiation and which encodes the major isoform of skeletal muscle alpha-tropomyosin. cDNA clone cC102 corresponds to a 2-kilobase RNA which is abundant in cultured embryonic skin fibroblasts and which encodes one of two alpha-tropomyosin-related fibroblast tropomyosins of 35,000 and 34,000 daltons apparent molecular mass (class 1 tropomyosins). The cC102 protein is unique among reported nonstriated-muscle tropomyosins in being identical in amino acid sequence to the major isoform of skeletal muscle alpha-tropomyosin over an uninterrupted stretch of at least 183 amino acids (residues 75-257). The two protein sequences differ in the COOH-terminal region beginning with residue 258. Because the cC101 and cC102 RNAs share an extensive region (at least 373 nucleotides) of nucleotide sequence identity upstream of the codon for residue 258, they are likely derived from a single gene by alternative RNA splicing, as was recently proposed in the case of related beta-tropomyosin mRNAs in human fibroblasts and skeletal muscle (MacLeod, A. R., Houlker, C., Reinach, R. C., Smillie, L. B., Talbot, K., Modi, G., and Walsh, F. S. (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 7835-7837). No alpha-tropomyosin-related RNAs are abundant in undifferentiated myoblasts. This suggests the possibility of a fibroblast-specific function, as opposed to a general nonmuscle-cell function for class 1 tropomyosins and also has implications for the regulation of alpha-tropomyosin gene expression during embryonic development.
我们描述了对两个鹌鹑cDNA克隆的分析，这两个克隆代表了不同但密切相关的α-原肌球蛋白mRNA。cDNA克隆cC101对应于一个1.2千碱基的RNA，它在成肌细胞分化过程中积累到高水平，并且编码骨骼肌α-原肌球蛋白的主要异构体。cDNA克隆cC102对应于一个2千碱基的RNA，它在培养的胚胎皮肤成纤维细胞中丰富，并且编码两种与α-原肌球蛋白相关的成纤维细胞原肌球蛋白之一，其表观分子量为35,000和34,000道尔顿（1类原肌球蛋白）。cC102蛋白在已报道的非横纹肌原肌球蛋白中是独特的，因为在至少183个氨基酸的不间断序列（第75 - 257位残基）上，其氨基酸序列与骨骼肌α-原肌球蛋白的主要异构体相同。这两种蛋白质序列在从第258位残基开始的COOH末端区域有所不同。由于cC101和cC102 RNA在第258位残基的密码子上游共享一个广泛的核苷酸序列同一性区域（至少373个核苷酸），它们可能是通过选择性RNA剪接从单个基因衍生而来的，就像最近在人类成纤维细胞和骨骼肌中相关β-原肌球蛋白mRNA的情况所提出的那样（MacLeod, A. R., Houlker, C., Reinach, R. C., Smillie, L. B., Talbot, K., Modi, G., and Walsh, F. S. (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 7835 - 7837）。未分化的成肌细胞中没有丰富的α-原肌球蛋白相关RNA。这表明1类原肌球蛋白可能具有成纤维细胞特异性功能，而不是一般的非肌肉细胞功能，并且这也对胚胎发育过程中α-原肌球蛋白基因表达的调控有影响。
