Boyne J R, Yosuf H M, Bieganowski P, Brenner C, Price C
Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, PO Box 594, Western Bank, Sheffield S10 2TN, UK.
J Cell Sci. 2000 Dec;113 Pt 24:4533-43. doi: 10.1242/jcs.113.24.4533.
MLC1 (myosin light chain) acts as a dosage suppressor of a temperature sensitive mutation in the gene encoding the S. cerevisiae IQGAP protein. Both proteins localize to the bud neck in mitosis although Mlc1p localisation precedes Iqg1p. Mlc1p is also found at the incipient bud site in G(1) and the growing bud tip during S and G(2) phases of the cell cycle. A dominant negative GST-Mlc1p fusion protein specifically blocks cytokinesis and prevents Iqg1p localisation to the bud neck, as does depletion of Mlc1p. These data support a direct interaction between the two proteins and immunoprecipitation experiments confirm this prediction. Mlc1p is also shown to interact with the class II conventional myosin (Myo1p). All three proteins form a complex, however, the interaction between Mlc1p and Iqg1p can be separated from the Mlc1p/Myo1p interaction. Mlc1p localisation and maintenance at the bud neck is independent of actin, Myo1p and Iqg1p. It is proposed that Mlc1p therefore functions to recruit Iqg1p and in turn actin to the actomyosin ring and that it is also required for Myo1p function during ring contraction.
肌球蛋白轻链1（MLC1）作为酿酒酵母IQGAP蛋白编码基因中温度敏感突变的剂量抑制因子。在有丝分裂过程中，这两种蛋白都定位于芽颈，尽管Mlc1p的定位先于Iqg1p。在细胞周期的G1期，Mlc1p也存在于起始芽位点，在S期和G2期存在于生长的芽尖。一种显性负性GST-Mlc1p融合蛋白特异性地阻断胞质分裂，并阻止Iqg1p定位于芽颈，Mlc1p的缺失也会导致同样的结果。这些数据支持了这两种蛋白之间存在直接相互作用，免疫沉淀实验证实了这一预测。Mlc1p还被证明与II类传统肌球蛋白（Myo1p）相互作用。这三种蛋白形成一个复合物，然而，Mlc1p和Iqg1p之间的相互作用可以与Mlc1p/Myo1p相互作用分开。Mlc1p在芽颈的定位和维持独立于肌动蛋白、Myo1p和Iqg1p。因此，有人提出Mlc1p的功能是将Iqg1p进而将肌动蛋白募集到肌动球蛋白环，并且在环收缩过程中Myo1p的功能也需要它。
