Proton total cross-sections on 1^{1}H, 2^{2}D, 4^{4}He, 12^{12}C, and 16^{16}O in the energy range 180 to 560 MeV

Proton total cross-sections on /sup 1/H, /sup 2/D, /sup 4/He, /sup 12 /C, and /sup 16/O have been measured in the energy range 180 to 560 Me V in a high precision transmission experiment with a statistical accuracy of +or-0.2%. Random errors are typically +or-0.5% for pp data, +or-1% for /sup 2/D and /sup 4/He, and +or-(1-3%) for /sup 12/C and /sup 16/O total cross-sections. Systematic errors of +or-(0.8-1%) in the /sup 1/H and /sup 2/D data originate mainly from uncertainties in applying the correct Coulomb-nuclear interference corrections to the measured partial cross-sections before extrapolating to the total cross-section at zero solid angle. The real parts of the nuclear spin- independent forward scattering amplitudes on /sup 4/He, /sup 12/C, and /sup 16/O were obtained in the same experiment by analysing the angular dependence of the partial cross-sections in the Coulomb- nuclear interference region. Total cross-sections are calculated in a Glauber-model approach, and the results are compared to this data

G1/S Cyclin-dependent Kinase Regulates Small GTPase Rho1p through Phosphorylation of RhoGEF Tus1p in Saccharomyces cerevisiae

Rho1p is an essential small GTPase that plays a key role in the morphogenesis of Saccharomyces cerevisiae. We show here that the activation of Rho1p is regulated by a cyclin-dependent kinase (CDK). Rho1p is activated at the G1/S transition at the incipient-bud sites by the Cln2p (G1 cyclin) and Cdc28p (CDK) complex, in a process mediated by Tus1p, a guanine nucleotide exchange factor for Rho1p. Tus1p interacts physically with Cln2p/Cdc28p and is phosphorylated in a Cln2p/Cdc28p-dependent manner. CDK phosphorylation consensus sites in Tus1p are required for both Cln2p-dependent activation of Rho1p and polarized organization of the actin cytoskeleton. We propose that Cln2p/Cdc28p-dependent phosphorylation of Tus1p is required for appropriate temporal and spatial activation of Rho1p at the G1/S transition