Orfa Rojas M, Wasserman M
Facultad de Ciencias Universidad Nacional, Bogotá, Colombia.
J Biochem. 1995 Dec;118(6):1118-23. doi: 10.1093/oxfordjournals.jbchem.a124996.
We studied the synthesis of calmodulin mRNA and of calmodulin during the asexual cell cycle of Plasmodium falciparum. The expression of the gene was low during the early stages of the erythrocytic asexual cycle. When the parasites were 28 h old the level of mRNA increased steadily to reach a peak at the age of 40 h. During the last 8 h of the cycle a constant decrease in the amount of calmodulin mRNA was observed. The synthesis of the protein followed the expression pattern of the mRNA, but without the final decrease. The average amounts of calmodulin measured were 2.5 +/- 0.9 ng/10(8) 14-h-old rings, 4.38 +/- 0.35 ng/10(8) 36-h-old trophozoites, 11.8 +/- 1.45 ng/10(8) 44-h-old trophozoites, and 19.6 +/- 1.9 ng/10(8) 48-h-old schizonts. The in vivo stability of mRNA in different developmental stages was evaluated by pulse and chase experiments. The RNA of very mature trophozoites was quickly degraded, in contrast with the high stability shown by the RNA in other stages. The results here suggest that the calmodulin gene expression in Plasmodium does not follow a housekeeping pattern of expression such as in other eukaryotic cells, but that it is regulated at the level of transcription and RNA degradation.
我们研究了恶性疟原虫无性细胞周期中钙调蛋白mRNA及钙调蛋白的合成。在红细胞无性周期的早期阶段，该基因的表达水平较低。当疟原虫发育至28小时龄时，mRNA水平稳步上升，并在40小时龄时达到峰值。在周期的最后8小时内，观察到钙调蛋白mRNA的量持续下降。蛋白质的合成遵循mRNA的表达模式，但没有最后的下降阶段。所测得的钙调蛋白平均量分别为：14小时龄环状体为2.5±0.9 ng/10⁸个；36小时龄滋养体为4.38±0.35 ng/10⁸个；44小时龄滋养体为11.8±1.45 ng/10⁸个；48小时龄裂殖体为19.6±1.9 ng/10⁸个。通过脉冲追踪实验评估了不同发育阶段mRNA在体内的稳定性。与其他阶段RNA所显示的高稳定性相反，非常成熟的滋养体的RNA迅速降解。这里的结果表明，疟原虫中钙调蛋白基因的表达并不遵循如其他真核细胞那样的持家基因表达模式，而是在转录和RNA降解水平受到调控。
