Polarized growth requires the integration of polarity pathways with the delivery of exocytic vesicles for cell expansion and counterbalancing endocytic uptake. In budding yeast, the myosin-V Myo2 is aided by the kinesin-related protein Smy1 in carrying out the essential Sec4-dependent transport of secretory vesicles to sites of polarized growth. Over-expression suppressors of a conditional myo2 smy1 mutant identified a novel F-BAR-containing RhoGAP, Rgd3, that has activity primarily on Rho3, but also Cdc42. Internally tagged Rho3 is restricted to the plasma membrane in a gradient corresponding to cell polarity that is altered upon Rgd3 over-expression. Rgd3 itself is localized to dynamic polarized vesicles that, while distinct from constitutive secretory vesicles, are dependent on actin and Myo2 function. In vitro Rgd3 associates with liposomes in a PIP₂-enhanced manner. Further, the Rgd3 C-terminal region contains several phosphorylatable residues within a reported SH3-binding motif. An unphosphorylated mimetic construct is active and highly polarized, while the phospho-mimetic form is not. Rgd3 is capable of activating Myo2, dependent on its phospho-state and Rgd3 overexpression rescues aberrant Rho3 localization and cell morphologies seen at the restrictive temperature in the myo2 smy1 mutant. We propose a model where Rgd3 functions to modulate and maintain Rho3 polarity during growth.

极化生长需要极性途径与胞外小泡的传递整合，以进行细胞扩增和平衡内吞摄取。在发芽的酵母中，肌球蛋白-V Myo2受到驱动蛋白相关蛋白Smy1的协助，将分泌小泡的必要的Sec4依赖性转运到极化生长位点。有条件的myo2 smy1突变体的过表达抑制因子鉴定出了一种新型的含F-BAR的RhoGAP Rgd3，其主要对Rho3具有活性，但对Cdc42也具有活性。内部标记的Rho3以对应于细胞极性的梯度限制在质膜上，该梯度随Rgd3过表达而改变。Rgd3本身位于动态极化的囊泡，虽然与组成型分泌囊泡不同，但它依赖于肌动蛋白和Myo2功能。体外Rgd3以PIP ₂增强的方式与脂质体缔合。此外，Rgd3 C端区域在报道的SH3结合基序内包含几个可磷酸化的残基。未磷酸化的模拟物构建体具有活性且高度极化，而磷酸化的模拟形式则没有。Rgd3能够激活Myo2，具体取决于其磷酸状态，而Rgd3的过表达可以挽救在myo2 smy1突变体的限制性温度下出现的异常Rho3定位和细胞形态。我们提出了一个模型，其中Rgd3在生长过程中起着调节和维持Rho3极性的作用。