The LIM Domain-Containing Dbm1 GTPase-Activating Protein Is Required for Normal Cellular Morphogenesis in Saccharomyces cerevisiae

Abstract

Normal cell growth in the yeast Saccharomyces cerevisiae involves the selection of genetically determined bud sites where most growth is localized. Previous studies have shown that BEM2, which encodes a GTPaseactivating protein (GAP) that is specific for the Rho-type GTPase Rho1p in vitro, is required for proper bud site selection and bud emergence. We show here that DBM1, which encodes another putative Rho-type GAP with two tandemly arranged cysteine-rich LIM domains, also is needed for proper bud site selection, as haploid cells lacking Dbm1p bud predominantly in a bipolar, rather than the normal axial, manner. Furthermore, yeast cells lacking both Bem2p and Dbm1p are inviable. The nonaxial budding defect of dbm1 mutants can be rescued partially by overproduction of Bem3p and is exacerbated by its absence. Since Bem3p has previously been shown to function as a GAP for Cdc42p, and also less efficiently for Rho1p, our results suggest that Dbm1p, like Bem2p and Bem3p, may function in vivo as a GAP for Cdc42p and/or Rho1p. Both LIM domains of Dbm1p are essential for its normal function. Point mutations that alter single conserved cysteine residues within either LIM domain result in mutant forms of Dbm1p that can no longer function in bud site selection but instead are capable of rescuing the inviability of bem2 mutants at 35؇C.

Regulation of Cdc42 polarization by the Rsr1 GTPase and Rga1, a Cdc42 GTPase-activating protein, in budding yeast

“…6B). When we counted only those cells that had more than two bud scars (that were spaced separately), a significant number of rga1Δ cells exhibited the bipolar pattern (62%, n=50), as previously reported (Chen et al, 1996;Smith et al, 2002;Stevenson et al, 1995). Because bud scars within a bud scar were sometimes less clear from static images (see Fig.…”

“…Because Cdc42 GAP(s) are likely to affect the dissociation rate of Cdc42 from the plasma membrane to the cytoplasm, we considered Rga1, which is the only Cdc42 GAP that specifically affects the axial budding pattern (Chen et al, 1996;Smith et al, 2002;Stevenson et al, 1995;Tong et al, 2007). Although it has been shown that Rga1 blocks Cdc42 polarization at the division site (Tong et al, 2007), it is unclear when Rga1 functions relative to the two steps of Cdc42 activation and whether Rga1 activity is involved in the fluctuating levels of Cdc42-GTP around the division site during T1.…”

“…The axial landmark then interacts with Bud5 to direct axial budding in haploid cells (Kang et al, 2012;Kang et al, 2001;Marston et al, 2001). In addition to the axial landmark, Rga1 affects the selection of a proper bud site (Chen et al, 1996;Smith et al, 2002;Stevenson et al, 1995;Tong et al, 2007). Rga1 inhibits polarization of Cdc42 within the division site and thus prevents re-budding at the same bud site (Tong et al, 2007).…”

Morphogenesis and the Cell Cycle

“…The yeast genome encodes 11 proteins with Rho-GAP domains. Genetic analyses suggested that three of these (Bem3p, Rga1p, and Rga2p) might be Cdc42p-specific and that their GAP domains catalyze GTP hydrolysis by Cdc42p in vitro (Bender and Pringle 1991;Zheng et al 1993Zheng et al , 1994Stevenson et al 1995;Chen et al 1996;Gladfelter et al 2002;Smith et al 2002). A fourth Rho-GAP (Bem2p) with genetic links to Cdc42p was initially thought to be selective for Rho1p (Zheng et al 1993), but was later shown to act on Cdc42p as well, at least in vitro (Marquitz et al 2002).…”

A Novel Connection between the Yeast Cdc42 GTPase and the Slt2-mediated Cell Integrity Pathway Identified through the Effect of Secreted Salmonella GTPase Modulators

“…Among the known upstream components, members of the Rho family of the small G proteins, such as Cdc42, have been identified as important modulators of MAPK cascades in S. cerevisiae (1). Whereas Cdc24 is believed to be the sole GEF for Cdc42 (1,14), three proteins have been proposed to be GAPs for Cdc42: Bem3, which has been shown to have GAP activity against Cdc42 in vitro (15, 16), Rga1/Dbm1 (17,18), and Rga2, which is identified by its homology to Rga1 (1).…”