Kinetic and Structural Analysis of the Mg2+ -binding Site of the Guanine Nucleotide-binding Protein p21 H-ras.

The coordination and binding of the Mg2+ ion in the nucleotide−binding site of p21 have been investigated using site−directed mutagenesis, kinetic methods, and phosphorous NMR. Mg2+ in the p21.nucleotide.Mg2+ complex appears to be in fast equilibrium with the solvent. The dissociation constant between Mg2+ and the p21.GDP complex was determined to be 2.8 microM. It decreases 30− or 16−fold on substituting Ser−17 or Asp−57 with alanine, respectively, whereas the T35A mutation has no effect. All three mutations influence the dissociation constants and the association and dissociation rate constants of the interaction between guanine nucleotides and p21, but to a different degree. We conclude that Thr−35 is only complexed to Mg2+ in the GTP conformation and both Asp−57 and Ser−17 appear to be critical for both GDP and GTP binding. 31P NMR spectra of the GDP and Gpp(NH)p (guanosine−5'−(beta,gamma−imido)triphosphate) complexes of mutated p21 show a remarkable perturbation of the guanine nucleotide− binding site compared to wild−type protein. The mutant proteins show reduced GTPase rates, which are not stimulated by the GTPase−activating protein GAP. p21(S17A) has been reported to function just as p21(S17N) as a dominant negative inhibitor of normal p21. We find that it inhibits oncogenic p21−induced survival of primary neuron

Incentive to reduce crop trait durability

Inbred line seed producers face competition from their own consumers: farmers who save part of their harvest can costly self-produce. To reduce this competition, seed producers can switch to non-durable hybrid seed production. In a two-period model, we investigate what is the impact of crop durability on self-production, pricing strategies and switching decision. We first study the pricing decisions and switching decisions of an inbred line seed monopoly. Then, we analyze how the monopoly's behavior is affected by the entry of a hybrid seed producer. We also examine how the introduction of royalties on farmers who self-produce improves efficiency. Our main finding is that, for some constellation of costs, an inbred line seed monopoly has an incentive to produce technologically dominated hybrid seed in order to extract more surplus from farmers. Along the same lines, an inbred line monopoly has an incentive to let a hybrid seed producer enters the market for discrimination purposes.Crop Production/Industries,

Radiative corrections to the Dalitz plot of K_{l3}^\pm decays

We calculate the model-independent radiative corrections to the Dalitz plot of K_{l3}^\pm decays to order (\alpha/\pi)(q/M_1), where q is the momentum transfer and M_1 is the mass of the kaon. The final results are presented, first, with the triple integration over the variables of the bremsstrahlung photon ready to be performed numerically and, second, in an analytical form. These two forms are useful to crosscheck on one another and with other calculations. This paper is organized to make it accessible and reliable in the analysis of the Dalitz plot of precision experiments and is not compromised to fixing the form factors at predetermined values. It is assumed that the real photons are kinematically discriminated. Otherwise, our results have a general model-independent applicability.Comment: RevTex4, 38 pages, 5 figures, 5 tables; some typos corrected; discussion extended to compare with other result

Matching pre-equilibrium dynamics and viscous hydrodynamics

We demonstrate how to match pre-equilibrium dynamics of a 0+1 dimensional quark gluon plasma to 2nd-order viscous hydrodynamical evolution. The matching allows us to specify the initial values of the energy density and shear tensor at the initial time of hydrodynamical evolution as a function of the lifetime of the pre-equilibrium period. We compare two models for the pre-equilibrium quark-gluon plasma, longitudinal free streaming and collisionally-broadened longitudinal expansion, and present analytic formulas which can be used to fix the necessary components of the energy-momentum tensor. The resulting dynamical models can be used to assess the effect of pre-equilibrium dynamics on quark-gluon plasma observables. Additionally, we investigate the dependence of entropy production on pre-equilibrium dynamics and discuss the limitations of the standard definitions of the non-equilibrium entropy.Comment: 24 pages, 5 figures,v2: minor modifications and updated references. Accepted for publication in Phys. Rev.

Massive gravity: nonlinear instability of the homogeneous and isotropic universe

We argue that all homogeneous and isotropic solutions in nonlinear massive gravity are unstable. For this purpose, we study the propagating modes on a Bianchi type--I manifold. We analyze their kinetic terms and dispersion relations as the background manifold approaches the homogeneous and isotropic limit. We show that in this limit, at least one ghost always exists and that its frequency tends to vanish for large scales, meaning that it cannot be integrated out from the low energy effective theory. This ghost mode is interpreted as a leading nonlinear perturbation around a homogeneous and isotropic background.Comment: 4 pages, uses REVTeX4.1; v2: minor update to match the published versio