Ling K Y, Preston R R, Burns R, Kink J A, Saimi Y, Kung C
Laboratory of Molecular Biology, University of Wisconsin, Madison 53706.
Proteins. 1992 Apr;12(4):365-71. doi: 10.1002/prot.340120408.
Paramecium tetraurelia behavioral mutant cam12 displays a "fast-2" behavioral phenotype: it fails to respond to Na+ stimuli. Electrophysiologically, it lacks a Ca(++)-dependent Na+ current. Genetics and DNA sequencing showed the primary defect of cam12 to be in the calmodulin gene (Kink et al., 1990). To correlate calmodulin structure and function in Paramecium, we elucidated the primary structure of cam12 calmodulin. Peptide sequencing confirmed the two point mutations predicted by the DNA sequence: a glycine-to-glutamate substitution at position 40 and an aspartate-to-asparagine substitution at position 50. Our results further showed that lysine 13 and lysine 115 were methylated normally in cam12. It is likely that the electrophysiological abnormalities of cam12 are a direct reflection of the amino-acid substitutions, as opposed to improper posttranslational modification.
四膜虫行为突变体cam12表现出“快速-2”行为表型：它对钠离子刺激无反应。在电生理方面，它缺乏一种钙离子依赖性钠离子电流。遗传学和DNA测序表明，cam12的主要缺陷在于钙调蛋白基因（金克等人，1990年）。为了关联四膜虫中钙调蛋白的结构与功能，我们阐明了cam12钙调蛋白的一级结构。肽段测序证实了DNA序列预测的两个点突变：第40位的甘氨酸被谷氨酸取代，第50位的天冬氨酸被天冬酰胺取代。我们的结果还表明，cam12中第13位赖氨酸和第115位赖氨酸的甲基化正常。cam12的电生理异常很可能是氨基酸取代的直接反映，而非翻译后修饰不当所致。
