Chaudhari N
Department of Physiology, Colorado State University, Fort Collins 80523.
J Biol Chem. 1992 Dec 25;267(36):25636-9.
The skeletal muscle-specific dihydropyridine-sensitive calcium channel is a critical component of excitation-contraction coupling in skeletal muscle. A recessive mutation in mice, muscular dysgenesis (mdg), has previously been described as resulting in defective excitation-contraction coupling. Although the channel-forming subunit (alpha 1) of the skeletal calcium channel is not detectable immunologically, specific mRNA of normal size is present in dysgenic muscle. cDNA for this calcium channel alpha 1 subunit has now been cloned from dysgenic muscle and sequenced in its entirety. A single nucleotide deletion occurs at nucleotide 4010 of the cDNA, resulting in a shift of the translational reading frame. The mutation has been confirmed by direct sequencing of PCR products from homozygous mutant and normal muscle. The mutant polypeptide is predicted to contain the first three repeating domains, five of the normal six transmembrane helices of the last repeating domain, and an altered and truncated C terminus. The mature mRNA encoding the dysgenic alpha 1 subunit appears to be labile. It is possible that premature termination of translation renders the mutant mRNA subject to degradation by nucleases. This work resolves a long-standing controversy on the nature of the primary genetic defect in muscular dysgenesis.
骨骼肌特异性二氢吡啶敏感钙通道是骨骼肌兴奋-收缩偶联的关键组成部分。小鼠中的一种隐性突变，即肌肉发育不全（mdg），先前已被描述为导致兴奋-收缩偶联缺陷。尽管骨骼肌钙通道的通道形成亚基（α1）在免疫学上无法检测到，但正常大小的特异性mRNA存在于发育不全的肌肉中。现在已经从发育不全的肌肉中克隆出了这种钙通道α1亚基的cDNA，并对其进行了全序列测定。在cDNA的第4010个核苷酸处发生了一个单核苷酸缺失，导致翻译阅读框的移位。通过对来自纯合突变体和正常肌肉的PCR产物进行直接测序，证实了该突变。预测突变多肽包含前三个重复结构域、最后一个重复结构域正常六个跨膜螺旋中的五个，以及一个改变和截短的C末端。编码发育不全α1亚基的成熟mRNA似乎不稳定。翻译的过早终止可能使突变mRNA易受核酸酶降解。这项工作解决了关于肌肉发育不全原发性遗传缺陷本质的长期争议。
