State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China.
PLoS One. 2013 Jun 13;8(6):e66321. doi: 10.1371/journal.pone.0066321. Print 2013.
Msb1 is not essential for growth in the budding yeast Saccharomyces cerevisiae since msb1Δ cells do not display obvious phenotypes. Genetic studies suggest that Msb1 positively regulates Cdc42 function during bud development, since high-copy MSB1 suppressed the growth defect of temperature-sensitive cdc24 and cdc42 mutants at restrictive temperature, while deletion of MSB1 showed synthetic lethality with cdc24, bem1, and bem2 mutations. However, the mechanism of how Msb1 regulates Cdc42 function remains poorly understood. Here, we show that Msb1 localizes to sites of polarized growth during bud development and interacts with Cdc42 in the cells. In addition, Msb1 interacts with Boi1 and Boi2, two scaffold proteins that also interact with Cdc42 and Bem1. These findings suggest that Msb1 may positively regulate Cdc42 function by interacting with Cdc42, Boi1, and Boi2, which may promote the efficient assembly of Cdc42, Cdc24, and other proteins into a functional complex. We also show that Msb1 interacts with Rho1 in the cells and Msb1 overproduction inhibits the growth of rho1-104 and rho1-3 but not rho1-2 cells. The growth inhibition appears to result from the down-regulation of Rho1 function in glucan synthesis, specifically during early stage of bud development. These results suggest that Msb1 may coordinate Cdc42 and Rho1 functions during early stage of bud development by promoting Cdc42 function and inhibiting Rho1 function. Msb1 overproduction also affects cell morphology, septin organization, and causes increased, aberrant deposition of 1,3-β-glucan and chitin at the mother-bud neck. However, the stimulation of glucan synthesis mainly occurs during late, but not early, stage of bud development.
Msb1 对于出芽酵母酿酒酵母的生长不是必需的，因为 msb1Δ 细胞没有表现出明显的表型。遗传研究表明，Msb1 在芽发育过程中正向调节 Cdc42 的功能，因为高拷贝 MSB1 抑制了温度敏感型 cdc24 和 cdc42 突变体在限制温度下的生长缺陷，而 MSB1 的缺失与 cdc24、bem1 和 bem2 突变体表现出合成致死性。然而，Msb1 调节 Cdc42 功能的机制仍知之甚少。在这里，我们表明 Msb1 在芽发育过程中定位于极化生长的部位，并与细胞中的 Cdc42 相互作用。此外，Msb1 与 Boi1 和 Boi2 相互作用，Boi1 和 Boi2 是两种支架蛋白，也与 Cdc42 和 Bem1 相互作用。这些发现表明，Msb1 可能通过与 Cdc42、Boi1 和 Boi2 相互作用来正向调节 Cdc42 的功能，这可能促进 Cdc42、Cdc24 和其他蛋白质有效地组装成一个功能复合物。我们还表明，Msb1 在细胞中与 Rho1 相互作用，并且 Msb1 的过表达抑制 rho1-104 和 rho1-3 的生长，但不抑制 rho1-2 的生长。生长抑制似乎是由于 Rho1 在葡聚糖合成中的功能下调，特别是在芽发育的早期阶段。这些结果表明，Msb1 可能通过促进 Cdc42 功能和抑制 Rho1 功能来协调芽发育早期的 Cdc42 和 Rho1 功能。Msb1 的过表达也会影响细胞形态、隔膜组织，并导致在母-芽颈部过度且异常地沉积 1,3-β-葡聚糖和几丁质。然而，葡聚糖合成的刺激主要发生在芽发育的后期，而不是早期。
