Busch Karl Emanuel, Brunner Damian
European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany.
Curr Biol. 2004 Apr 6;14(7):548-59. doi: 10.1016/j.cub.2004.03.029.
CLIP-170 and EB1 protein family members localize to growing microtubule tips and link spatial information with the control of microtubule dynamics. It is unknown whether these proteins operate independently or whether their actions are coordinated. In fission yeast the CLIP-170 homolog tip1p is required for targeting of microtubules to cell ends, whereas the role of the EB1 homolog mal3p in microtubule organization has not been investigated.
We show that mal3p promotes the initiation of microtubule growth and inhibits catastrophes. Premature catastrophes occur randomly throughout the cell in the absence of mal3p. mal3p decorates the entire microtubule lattice and localizes to particles along the microtubules and at their growing tips. Particles move in two directions, outbound toward the cell ends or inbound toward the cell center. At cell ends, the microtubule tip-associated mal3p particles disappear followed by a catastrophe. mal3p localizes normally in tip1-deleted cells and disappears from microtubule tips preceding the premature catastrophes. In contrast, tip1p requires mal3p to localize at microtubule tips. mal3p and tip1p directly interact in vitro.
mal3p and tip1p form a system allowing microtubules to target cell ends. We propose that mal3p stimulates growth initiation and maintains growth by suppressing catastrophes. At cell ends, mal3p disappears from microtubule tips followed by a catastrophe. mal3p is involved in recruiting tip1p to microtubule tips. This becomes important when microtubules contact the cell cortex outside the cell ends because mal3p dissociates prematurely without tip1p, which is followed by a premature catastrophe.
CLIP - 170和EB1蛋白家族成员定位于正在生长的微管末端，并将空间信息与微管动力学控制联系起来。尚不清楚这些蛋白是独立发挥作用，还是其作用相互协调。在裂殖酵母中，微管靶向细胞末端需要CLIP - 170同源物tip1p，而EB1同源物mal3p在微管组织中的作用尚未得到研究。
我们发现mal3p促进微管生长的起始并抑制微管解聚。在没有mal3p的情况下，过早的微管解聚在整个细胞中随机发生。mal3p覆盖整个微管晶格，并定位于沿微管及其生长末端的颗粒上。颗粒沿两个方向移动，向外朝向细胞末端或向内朝向细胞中心。在细胞末端，与微管末端相关的mal3p颗粒消失，随后发生微管解聚。mal3p在缺失tip1的细胞中定位正常，并在过早的微管解聚之前从微管末端消失。相反，tip1p需要mal3p才能定位于微管末端。mal3p和tip1p在体外直接相互作用。
mal3p和tip1p形成一个系统，使微管能够靶向细胞末端。我们提出，mal3p通过抑制微管解聚来刺激生长起始并维持生长。在细胞末端，mal3p从微管末端消失，随后发生微管解聚。mal3p参与将tip1p招募到微管末端。当微管接触细胞末端以外的细胞皮层时，这一点变得很重要，因为没有tip1p时mal3p会过早解离，随后发生过早的微管解聚。
