Berman Steven A, Wilson Nedra F, Haas Nancy A, Lefebvre Paul A
Department of Plant Biology, University of Minnesota, 250 Biological Sciences Center, St. Paul, MN 55108, USA.
Curr Biol. 2003 Jul 1;13(13):1145-9. doi: 10.1016/s0960-9822(03)00415-9.
Little is known about the molecular basis of organelle size control in eukaryotes. Cells of the biflagellate alga Chlamydomonas reinhardtii actively maintain their flagella at a precise length. Chlamydomonas mutants that lose control of flagellar length have been isolated and used to demonstrate that a dynamic process keeps flagella at an appropriate length. To date, none of the proteins required for flagellar length control have been identified in any eukaryotic organism. Here, we show that a novel MAP kinase is crucial to enforcing wild-type flagellar length in C. reinhardtii. Null mutants of LF4 [2], a gene encoding a protein with extensive amino acid sequence identity to a mammalian MAP kinase of unknown function, MOK [3], are unable to regulate the length of their flagella. The LF4 protein (LF4p) is localized to the flagella, and in vitro enzyme assays confirm that the protein is a MAP kinase. The long-flagella phenotype of lf4 cells is rescued by transformation with the cloned LF4 gene. The demonstration that a novel MAP kinase helps enforce flagellar length control indicates that a previously unidentified signal transduction pathway controls organelle size in C. reinhardtii.
关于真核生物中细胞器大小控制的分子基础，人们了解甚少。双鞭毛藻类莱茵衣藻的细胞能积极地将其鞭毛维持在精确的长度。已分离出失去鞭毛长度控制的莱茵衣藻突变体，并用于证明一个动态过程使鞭毛保持在合适的长度。迄今为止，在任何真核生物中都尚未鉴定出鞭毛长度控制所需的蛋白质。在此，我们表明一种新型的丝裂原活化蛋白激酶（MAP激酶）对于维持莱茵衣藻野生型鞭毛长度至关重要。LF4 [2]的缺失突变体，LF4是一个基因，其编码的蛋白质与功能未知的哺乳动物MAP激酶MOK [3]具有广泛的氨基酸序列同一性，该突变体无法调节其鞭毛的长度。LF4蛋白（LF4p）定位于鞭毛，体外酶活性测定证实该蛋白是一种MAP激酶。通过用克隆的LF4基因转化可挽救lf4细胞的长鞭毛表型。一种新型MAP激酶有助于实施鞭毛长度控制这一证明表明，一条先前未被识别的信号转导途径控制着莱茵衣藻中的细胞器大小。
