Bni1p and Bnr1p: downstream targets of the Rho family small G-proteins which interact with profilin and regulate actin cytoskeleton in Saccharomyces cerevisiae

Abstract

The RHO1 gene encodes a homologue of mammalian remains to be clarified whether these target proteins of RhoA small G-protein in the yeast Saccharomyces Rho are involved in the reorganization of actin cytocerevisiae. Rho1p is required for bud formation and is skeleton. Very recently, one of these proteins, Rho kinase, localized at a bud tip or a cytokinesis site. We have recently shown that Bni1p is a potential target of has been shown to inhibit the myosin phosphatase activity Rho1p. Bni1p shares the FH1 and FH2 domains with (Kimura et al., 1996), although its physiological significproteins involved in cytokinesis or establishment of ance remains to be clarified. cell polarity. In S.cerevisiae, there is an open reading Cells of the budding yeast Saccharomyces cerevisiae frame (YIL159W) which encodes another protein grow by budding for cell division, and the actin cytohaving the FH1 and FH2 domains and we have named skeleton plays a pivotal role in the budding process this gene BNR1 (BNI1 Related). Bnr1p interacts with (Drubin, 1991 Johnson and Pringle, 1990). mutant shows a severe temperature-sensitive growth RHO1 is a homologue of the mammalian RhoA gene and phenotype. Cells of the bni1 bnr1 mutant arrested we have shown that the rho1 mutants are deficient in at the restrictive temperature are deficient in bud the budding process (Yamochi et al., 1994). Moreover, emergence, exhibit a random distribution of cortical immunofluorescence microscopic studies indicate that actin patches and often become multinucleate. TheseRho1p is localized at the growth site with cortical actin phenotypes are similar to those of the mutant of patches, including the presumptive budding site, the bud PFY1, which encodes profilin, an actin-binding protein.tip and the cytokinesis site (Yamochi et al., 1994). These Moreover, yeast two-hybrid and biochemical studies results suggest that RHO1 regulates the processes of bud demonstrate that Bni1p and Bnr1p interact directly formation. Concerning the downstream targets of Rho1p, with profilin at the FH1 domains. These results indicate we have shown that one of them is a homologue of that Bni1p and Bnr1p are potential targets of the Rho mammalian protein kinase C, Pkc1p (Nonaka et al., 1995), family members, interact with profilin and regulate which regulates cell wall integrity through the activation the reorganization of actin cytoskeleton.of the MAP kinase cascade (Levin and Errede, 1995). We Keywords: actin cytoskeleton/profilin/Rho have also shown that another target of Rho1p is 1,3-β-glucan synthase (Drgonová et al., 1996;Qadota et al., 1996), which is involved in cell wall synthesis. Very recently, we have identified BNI1 as a third potential target

Stable and Dynamic Axes of Polarity Use Distinct Formin Isoforms in Budding Yeast

“…However, strains lacking Bnr1p still transport vesicles from the mother to concentrate at the bud tip ( Figure 3A) and are able to grow with a normal morphology and rate (Imamura et al, 1997;Vallen et al, 2000), suggesting that the few Bni1p-dependent cables in the mother cell meet the transport requirements of the yeast cell under the conditions examined so far.…”

“…The FH1 region is a proline-rich stretch that recruits profilin, an actin-monomer binding protein essential for formin function in vivo , to participate in FH2-mediated nucleation in vitro (Sagot et al, 2002b;Kovar et al, 2003;Pring et al, 2003). Other regions present in Bni1p and Bnr1p are a regulatory NH 2 -terminal rho-GTPase-binding domain that subjects many formins to rho-dependent activation (Kohno et al, 1996;Evangelista et al, 1997;Imamura et al, 1997;Dong et al, 2003), and an FH3 motif that helps localize formins within the cell (Petersen et al, 1998).…”

“…The FH1 region is a proline-rich stretch that recruits profilin, an actin-monomer binding protein essential for formin function in vivo , to participate in FH2-mediated nucleation in vitro (Sagot et al, 2002b;Kovar et al, 2003;Pring et al, 2003). Other regions present in Bni1p and Bnr1p are a regulatory NH 2 -terminal rho-GTPase-binding domain that subjects many formins to rho-dependent activation (Kohno et al, 1996;Evangelista et al, 1997;Imamura et al, 1997;Dong et al, 2003), and an FH3 motif that helps localize formins within the cell (Petersen et al, 1998).With loss of formin function, actin cables disassemble in 2 min, and a cytokinetic ring is unable to assemble, but actin patches remain intact Sagot et al, 2002a;Tolliday et al, 2002). Other actin nucleators, particularly the Arp2/3 complex, play no apparent role in cable or cytokinetic ring assembly in budding yeast (Winter et al, 1999;Evangelista et al, 2002;Tolliday et al, 2002), suggesting the formins might be in vivo nucleators for these actin filaments.…”

Isolation and characterization of a novel actin filament-binding protein from Saccharomyces cerevisiae

“…Bni1p is known to be implicated in cytokinesis and establishment of cell polarity (Jansen et al, 1996;Zahner et al, 1996). We have moreover found that Bni1p directly interacts with pro®lin, an actin monomer-binding protein, which accelerates the polymerization of actin (Imamura et al, 1997). It is likely that Rho1p regulates the reorganization of the actin cytoskeleton through the Bni1p-pro®lin system in the budding yeast.…”

“…Rho1p regulates the reorganization of the actin cytoskeleton at least through the Bni1p-pro®lin system in the budding yeast (Kohno et al, 1996;Imamura et al, 1997). We have examined a possible interaction of ABP140 with Rho1p, Bni1p, and pro®lin by use of the yeast two-hybrid system.…”