Daisuke Watanabe

Movement of yeast 1,3‐β‐glucan synthase is essential for uniform cell wall synthesis

Background:  The cell wall has an important role in maintaining cell shape. In the budding yeast Saccharomyces cerevisiae, the major filamentous component of the cell wall responsible for its rigidity is 1,3‐β‐glucan and is synthesized by 1,3‐β‐glucan synthase (GS), localized on the plasma membrane.

Yeast Lrg1p acts as a specialized RhoGAP regulating 1,3‐β‐glucan synthesis

Selection of an extragenic suppressor of fks1‐1154 Δfks2, mutations in the catalytic subunits of yeast 1,3‐β‐glucan synthase (GS) conferring temperature‐sensitivity, led to the LRG1 gene, which was originally identified as a LIM‐RhoGAP homologous gene. Mutations in the LRG1 gene restore impaired 1,3‐β‐glucan synthesis in the fks1‐1154 Δfks2 mutant as well as that in rho1‐2, a temperature‐sensitive mutant of Rho‐type GTPase that functions as a regulatory subunit of GS. Two‐hybrid analyses of Lrg1p, which contains a sequence conserved among Rho GTPase‐activating proteins (GAPs), revealed its specific interactions with the active form of Rho1p. Among eight potential yeast RhoGAPs, Lrg1p is the only member that negatively regulates GS activity: mutations in the rest of GAPs, including bem2, Δbem3, Δsac7, Δbag7, Δrga1, Δrga2 and Δrgd1, do not suppress impairment of 1,3‐β‐glucan synthesis. Analyses of Mpk1p phosphorylation revealed the inability of Lrg1p to regulate the Pkc1p–MAP kinase cascade, a distinct Rho1p‐regulating signalling pathway known to be affected by the GAPs, Bem2p and Sac7p. Thus, different groups of Rho1p GAPs control the activity of different Rho1p‐effector proteins. Copyright

Comprehensive and quantitative analysis of yeast deletion mutants defective in apical and isotropic bud growth

To obtain a comprehensive understanding of the budding phase transition, 4,711 Saccharomyces cerevisiae haploid nonessential gene deletion mutants were screened with the image processing program CalMorph, and 35 mutants with a round bud and 173 mutants with an elongated bud were statistically identified. We classified round and elongated bud mutants based on factors thought to affect the duration of the apical bud growth phase. Two round bud mutants (arc18 and sac6) were found to be defective in apical actin patch localization. Several elongated bud mutants demonstrated a delay of cell cycle progression at the apical growth phase, suggesting that these mutants have a defect in the control of cell cycle progression.

Ion association dynamics in aqueous solutions of sulfate salts as studied by Raman band shape analysis

A new perspective is shown on the interaction between the sulfate ion and its counter cation in aqueous solutions. We propose the dynamic exchange model of ion association instead of the conventional static equilibrium model. The concentration dependence of the Raman band shape of the totally symmetric (a(1)) SO stretch mode of the sulfate ion is investigated systematically for four sulfate ions, MgSO(4), (NH(4))(2)SO(4), K(2)SO(4), and Li(2)SO(4). The concentration dependence of the a(1) Raman band shape in the MgSO(4) system is successfully reproduced by the analysis based on the dynamic exchange model. As a result, quantitative information about the extremely dynamic nature of the ion association has been obtained: the mean time between associations is a few picoseconds and the mean lifetime of association is several hundred femtoseconds.

Cell shape and growth of budding yeast cells in restrictive microenvironments

Effects of limited growth space on the cell morphology and cell growth are investigated by creating rigid outside environments. The cube‐shaped holes big enough for a single cell of the budding yeast Saccharomyces cerevisiae were prepared with a focused ion‐beam (FIB), commonly used for processing semiconductors. We demonstrated that the outline of the cells changes their ellipsoidal morphology into a cubic form when the daughter cells are grown in the holes, indicating that yeast cells change their shape in response to external limited space. The yeast cells grown in the microenvironments exhibit neither bud formation nor nuclear division. Although restricted growth caused by the physical barriers leads to the block of cell cycle progression in the wild‐type cells, swe1Δ cells defective in the morphogenesis checkpoint become binucleate after being grown in the microenvironments. These results suggest that yeast cells under spatial restriction arrest cell cycle progression in a Swelp‐dependent manner. Copyright

Carbonylative Polymerization of Oxetanes Initiated by Acetyl Cobalt Complexes

Four acetyl cobalt complexes, [AcCo(CO)(3)P(p-tolyl)(3)] (1; p-tolyl=4-Me-C(6)H(4)), [AcCo(CO)(3)P(OPh)(3)] (2), [AcCo(CO)(3)P(NMe(2))(3)] (3), and [AcCo(CO)(2)(dppp)] (4; dppp=1,3-bis(diphenylphosphanyl)propane), were synthesized, characterized, and examined as catalysts for the unprecedented carbonylative polymerization of oxetanes. Copolymers containing ester (4-hydroxyalkanoate) and/or ether units were obtained with complexes 1 and 2, but not with complexes 3 and 4 either in the presence or absence of additional phosphorus ligands. The ester unit/ether unit ratio varied in the range 21:79-63:37, and the highest ester/ether ratio of 63:37 was achieved by using complex 1 in the presence of a further 5 equivalents of P(OPh)(3). Although direct carbonylative polymerization is possible, preformation and ring opening of the gamma-lactone is also suggested as an alternative pathway.

Response to “Comment on ‘Ion association dynamics in aqueous solutions of sulfate salts as studied by Raman band shape analysis’ ” [J. Chem. Phys. 124, 247101 (2006)]

In this Response, answers are given, respectively, to the questions raised in the Comment by Buchner et al. [J. Chem. Phys.(to be published)]. We believe that, in the analysis of vibrational spectra in the liquid phase, dynamic viewpoints are necessary in order to fully understand their band shapes.