蛋白质的亚细胞定位与其生物学功能有密切的关系。以一个新的小鼠N5-谷氨酰胺甲基转移酶基因mHemk的两个转录剪接本mHemk1和mHemk2(GenBank编号分别为AY456393和AY583759)为材料,进一步分析了该蛋白的亚细胞定位。根据生物信息学预测, 在这两个蛋白质C-末端可能分别存在内质网(ER)定位信号RFSK和KSLK, 且这两个蛋白质都可能主要定位于细胞质。分别构建了这两个蛋白质以及相应的删除了C-末端RFSK和KSLK的缺失突变体与加强型绿色荧光蛋白的融合蛋白的表达质粒,并转染到MCF-7细胞中。结果证明mHemk1蛋白中的RFSK基序是一个新的内质网定位信号, 但没有足够的证据支持KSLK基序是mHemk2蛋白的内质网定位信号。这两个转录剪接本蛋白不同的亚细胞定位是否表明它们在不同的亚细胞器内有不同的功能仍值得深入研究。

The subcellular localization of protein is closely related to its biological function. Two splice variants of a novel mouse N5-glutamine methyltransferase gene mHemk, termed mHemk1 and mHemk2 (GenBank accession number AY456393 and AY583759, respectively), were cloned and identified previously. The subcellular localization of the proteins they encode was further analyzed. Bioinformatics analysis predicted a potential endoplasmic reticulum (ER) membrane-retention signal RFSK or KSLK at the C-terminus of mHemk1 or mHemk2 protein, and predicted a preferential cytoplasmic localization of the two splice variants. The plasmids were constructed to express the fusion proteins of the enhanced green fluorescent protein (EGFP) with each of the two splice variants and their mutants lacking the predicted ER-retention signals, and were transfected into the MCF-7 cells. Results confirmed that RFSK motif in mHemk1 protein is a novel ER-retention signal. Nevertheless, there was no strong evidence to support that KSLK motif is an ER-retention signal in mHemk2 protein. Whether the differential subcellular localization of the two mHemk splice variants indicates their different functions in distinct subcellular compartments is worth of further study.