Schmidt Anja, Schmelzle Tobias, Hall Michael N
Department of Biochemistry, Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland.
Mol Microbiol. 2002 Sep;45(5):1433-41. doi: 10.1046/j.1365-2958.2002.03110.x.
In Saccharomyces cerevisiae, the small GTPase RHO1 plays an essential role in the control of cell wall synthesis and organization of the actin cytoskeleton. Several regulators for RHO1 are known, including the GTPase-activating proteins (GAPs) SAC7 and BEM2. Here we show that BAG7, identified as the closest homologue of SAC7, also acts as a GAP for RHO1 in vitro and in vivo. Furthermore, we find that BAG7, SAC7, and BEM2 are functionally different in vivo. Overexpression of BAG7 or SAC7,but not BEM2, suppresses the cold sensitivity of a sac7 mutation and the lethality of RHO1 hyperactivation in response to cell wall damage. In contrast, overexpression of BEM2 or SAC7, but not BAG7, downregulates the RHO1-controlled PKC1-MPK1 pathway, and disruption of BEM2 or SAC7, but not BAG7, results in increased MPK1 activation. We conclude that BEM2 and SAC7, but not BAG7, are involved in the control of the RHO1-mediated activation of MPK1, whereas BAG7 and SAC7, but not BEM2, are involved in the regulation of other RHO1 functions. This suggests that different RHO1GAPs control different RHO1 effector pathways, thus ensuring their individual regulation at the appropriate place and time.
在酿酒酵母中，小GTP酶RHO1在细胞壁合成的控制和肌动蛋白细胞骨架的组织中起着至关重要的作用。已知几种RHO1的调节因子，包括GTP酶激活蛋白（GAPs）SAC7和BEM2。在此我们表明，被鉴定为SAC7最接近同源物的BAG7，在体外和体内也作为RHO1的GAP发挥作用。此外，我们发现BAG7、SAC7和BEM2在体内功能不同。BAG7或SAC7的过表达，但不是BEM2的过表达，可抑制sac7突变的冷敏感性以及RHO1因细胞壁损伤而过度激活的致死性。相反，BEM2或SAC7的过表达，但不是BAG7的过表达，会下调RHO1控制的PKC1 - MPK1途径，并且BEM2或SAC7的缺失，但不是BAG7的缺失，会导致MPK1激活增加。我们得出结论，BEM2和SAC7，但不是BAG7，参与RHO1介导的MPK1激活的控制，而BAG7和SAC7，但不是BEM2，参与其他RHO1功能的调节。这表明不同的RHO1 GAPs控制不同的RHO1效应途径，从而确保它们在适当的时间和地点进行个体调节。
