Identification of the Bud Emergence Gene BEM4 and Its Interactions with Rho-Type GTPases in Saccharomyces cerevisiae

Abstract

The Rho-type GTPase Cdc42p is required for cell polarization and bud emergence in Saccharomyces cerevisiae. To identify genes whose functions are linked to CDC42, we screened for (i) multicopy suppressors of a Ts ؊ cdc42 mutant, (ii) mutants that require multiple copies of CDC42 for survival, and (iii) mutations that display synthetic lethality with a partial-loss-of-function allele of CDC24, which encodes a guanine nucleotide exchange factor for Cdc42p. In all three screens, we identified a new gene, BEM4. Cells from which BEM4 was deleted were inviable at 37؇C. These cells became unbudded, large, and round, consistent with a model in which Bem4p acts together with Cdc42p in polarity establishment and bud emergence. In some strains, the ability of CDC42 to serve as a multicopy suppressor of the Ts ؊ growth defect of ⌬bem4 cells required co-overexpression of Rho1p, which is an essential Rho-type GTPase necessary for cell wall integrity. This finding suggests that Bem4p also affects Rho1p function. Bem4p displayed two-hybrid interactions with Cdc42p, Rho1p, and two of the three other known yeast Rho-type GTPases, suggesting that Bem4p can interact with multiple Rho-type GTPases. Models for the role of Bem4p include that it serves as a chaperone or modulates the interaction of these GTPases with one or more of their targets or regulators.

Activation of the nuclear factor-kappaB by Rho, CDC42, and Rac-1 proteins.

“…Furthermore, similar results were ob served with the human RhoB and RhoC proteins (results not shown), a further indication that it may be a com mon pathway for all Rho-related proteins. In keeping with this notion, it has been reported that at least in S. ceievisiae, a single protein, designated as BEM4, can in teract physically with several members of the Rho fam ily including Rho and CDC42 proteins (Mack et al 1996), suggesting that different members of the Rho fam ily may share some of their effectors.…”

Role of Small G Proteins in Yeast Cell Polarization and Wall Biosynthesis

“…Other Players BEM4 encodes a protein required for bud emergence at higher temperature (100). Because it interacts with constitutively active and dominant negative forms of Cdc42 as well as with Rho1, Rho2, and Rho4, its role in cell morphogenesis may be more general: e.g.…”

Is Ribosome Synthesis Controlled by Pol I Transcription?

“…27 FET3 encodes an integral membrane multicopper oxidase, which mediates resistance to copper ion toxicity. 28,29 BEM4 codes for a protein involved both in the establishment of cell polarity and bud emergence, in Rho protein signal transduction, 30 and in maintenance of proper telomere length. 31 Finally, the products of the last two genes are involved in mitochondrial metabolism: CBP3 encodes a mitochondrial chaperone required for assembly of the cytochrome bc1 complex 32,33 whereas MRLP24 codes for a mitochondrial RP of the large subunit.…”