Department of Genetics, University of Valencia, Valencia, Spain.
Mol Cells. 2010 Jul;30(1):65-70. doi: 10.1007/s10059-010-0089-9. Epub 2010 Jul 14.
Human Muscleblind-like proteins are alternative splicing regulators that are functionally altered in the RNA-mediated disease myotonic dystrophy. There are different Muscleblind protein isoforms in Drosophila and we previously determined that these have different subcellular localizations in the COS-M6 cell line. Here, we describe the conservation of the sequence motif KRAEK in isoforms C and E and propose a specific function for this motif. Different Muscleblind isoforms localize to the peri-plasma membrane (MblA), cytoplasm (MblB), or show no preference for the nuclear or cytoplasmic compartment (MblC and MblD) in Drosophila S2 cells transiently transfected with Musclebind expression plasmids. Mutation of the KRAEK motif reduces MblC nuclear localization, whereas fusion of a single KRAEK motif to the heterologous protein beta-galactosidase is sufficient to target the reporter protein to the nucleus of S2 cells. This motif is not exclusive to Muscleblind proteins and is detected in several other protein types. Taken together, these results suggest that the KRAEK motif regulates nuclear translocation of Muscleblind and may constitute a new class of nuclear localization signal.
人类肌肉萎缩相关蛋白是一种可变剪接调控因子，在 RNA 介导的疾病肌萎缩性侧索硬化症中其功能发生了改变。果蝇中有不同的肌肉萎缩蛋白异构体，我们之前已经确定这些在 COS-M6 细胞系中有不同的亚细胞定位。在这里，我们描述了异构体 C 和 E 中的 KRAEK 序列基序的保守性，并提出了该基序的特定功能。在转染肌肉萎缩蛋白表达质粒的果蝇 S2 细胞中，不同的肌肉萎缩蛋白异构体定位于质膜周围（MblA）、细胞质（MblB），或者对核或细胞质区室没有偏好（MblC 和 MblD）。KRAEK 基序的突变减少了 MblC 的核定位，而将单个 KRAEK 基序融合到异源蛋白β-半乳糖苷酶中足以将报告蛋白靶向 S2 细胞的核。这个基序不仅限于肌肉萎缩蛋白，在其他几种蛋白质类型中也有检测到。总之，这些结果表明，KRAEK 基序调节肌肉萎缩蛋白的核易位，可能构成了一类新的核定位信号。
