Irminger-Finger I, Hurt E, Roebuck A, Collart M A, Edelstein S J
Department of Biochemistry, University of Geneva, Switzerland.
J Cell Biol. 1996 Dec;135(5):1323-39. doi: 10.1083/jcb.135.5.1323.
The gene for a microtubule-associated protein (MAP), termed MHP1 (MAP-Homologous Protein 1), was isolated from Saccharomyces cerevisiae by expression cloning using antibodies specific for the Drosophila 205K MAP. MHP1 encodes an essential protein of 1,398 amino acids that contains near its COOH-terminal end a sequence homologous to the microtubule-binding domain of MAP2, MAP4, and tau. While total disruptions are lethal, NH2-terminal deletion mutations of MHP1 are viable, and the expression of the COOH-terminal two-thirds of the protein is sufficient for vegetative growth. Nonviable deletion-disruption mutations of MHP1 can be partially complemented by the expression of the Drosophila 205K MAP. Mhp1p binds to microtubules in vitro, and it is the COOH-terminal region containing the tau-homologous motif that mediates microtubule binding. Antibodies directed against a COOH-terminal peptide of Mhp1p decorate cytoplasmic microtubules and mitotic spindles as revealed by immunofluorescence microscopy. The overexpression of an NH2-terminal deletion mutation of MHP1 results in an accumulation of large-budded cells with short spindles and disturbed nuclear migration. In asynchronously growing cells that overexpress MHP1 from a multicopy plasmid, the length and number of cytoplasmic microtubules is increased and the proportion of mitotic cells is decreased, while haploid cells in which the expression of MHP1 has been silenced exhibit few microtubules. These results suggest that MHP1 is essential for the formation and/or stabilization of microtubules.
利用针对果蝇205K微管相关蛋白（MAP）的特异性抗体，通过表达克隆从酿酒酵母中分离出一种微管相关蛋白（MAP）的基因，命名为MHP1（MAP同源蛋白1）。MHP1编码一种由1398个氨基酸组成的必需蛋白，该蛋白在其COOH末端附近含有一段与MAP2、MAP4和tau的微管结合结构域同源的序列。虽然完全破坏是致死的，但MHP1的NH2末端缺失突变体是可行的，并且该蛋白COOH末端三分之二的表达足以支持营养生长。MHP1的不可行缺失破坏突变体可通过果蝇205K MAP的表达得到部分互补。Mhp1p在体外与微管结合，正是包含tau同源基序的COOH末端区域介导了微管结合。免疫荧光显微镜显示，针对Mhp1p的COOH末端肽的抗体可修饰细胞质微管和有丝分裂纺锤体。MHP1的NH2末端缺失突变体的过表达导致大芽细胞积累，纺锤体短且核迁移紊乱。在从多拷贝质粒过表达MHP1的异步生长细胞中，细胞质微管的长度和数量增加，有丝分裂细胞的比例降低，而MHP1表达被沉默的单倍体细胞几乎没有微管。这些结果表明，MHP1对微管的形成和/或稳定至关重要。
