Crossover recombination and synapsis are linked by adjacent regions within the N terminus of the Zip1 synaptonemal complex protein

Accurate chromosome segregation during meiosis relies on the prior establishment of at least one crossover recombination event between homologous chromosomes. Most meiotic recombination intermediates that give rise to interhomolog crossovers are embedded within a hallmark chromosomal structure called the synaptonemal complex (SC), but the mechanisms that coordinate the processes of SC assembly (synapsis) and crossover recombination remain poorly understood. Among known structural components of the budding yeast SC, the Zip1 protein is unique for its independent role in promoting crossover recombination; Zip1 is specifically required for the large subset of crossovers that also rely on the meiosis-specific MutSgamma complex. Here we report that adjacent regions within Zip1\u27s N terminus encompass its crossover and synapsis functions. We previously showed that deletion of Zip1 residues 21-163 abolishes tripartite SC assembly and prevents robust SUMOylation of the SC central element component, Ecm11, but allows excess MutSgamma crossover recombination. We find the reciprocal phenotype when Zip1 residues 2-9 or 10-14 are deleted; in these mutants SC assembles and Ecm11 is hyperSUMOylated, but MutSgamma crossovers are strongly diminished. Interestingly, Zip1 residues 2-9 or 2-14 are required for the normal localization of Zip3, a putative E3 SUMO ligase and pro-MutSgamma crossover factor, to Zip1 polycomplex structures and to recombination initiation sites. By contrast, deletion of Zip1 residues 15-20 does not detectably prevent Zip3\u27s localization at Zip1 polycomplex and supports some MutSgamma crossing over but prevents normal SC assembly and Ecm11 SUMOylation. Our results highlight distinct N terminal regions that are differentially critical for Zip1\u27s roles in crossing over and SC assembly; we speculate that the adjacency of these regions enables Zip1 to serve as a liaison, facilitating crosstalk between the two processes by bringing crossover recombination and synapsis factors within close proximity of one another

Model-Independent Semileptonic Form Factors Using Dispersion Relations

We present a method for parametrizing heavy meson semileptonic form factors using dispersion relations, and from it produce a two-parameter description of the B -> B elastic form factor. We use heavy quark symmetry to relate this function to B -> D* l nu form factors, and extract |V_cb|=0.0355^{+0.0029}_{-0.0025} from experimental data with a least squares fit. Our method eliminates model-dependent uncertainties inherent in choosing a parametrization for the extrapolation of the differential decay rate to threshold.Comment: uses lanlmac(harvmac) and epsf, 12 pages, 1 eps figure included (Talk by BG at the 6-th International Symposium on Heavy Flavour Physics, Pisa, Italy, 6--10 June, 1995

New Constraints on Dispersive Form Factor Parameterizations from the Timelike Region

We generalize a recent model-independent form factor parameterization derived from rigorous dispersion relations to include constraints from data in the timelike region. These constraints dictate the convergence properties of the parameterization and appear as sum rules on the parameters. We further develop a new parameterization that takes into account finiteness and asymptotic conditions on the form factor, and use it to fit to the elastic \pi electromagnetic form factor. We find that the existing world sample of timelike data gives only loose bounds on the form factor in the spacelike region, but explain how the acquisition of additional timelike data or fits to other form factors are expected to give much better results. The same parameterization is seen to fit spacelike data extremely well.Comment: 24 pages, latex (revtex), 3 eps figure

Theory of unitarity bounds and low energy form factors

We present a general formalism for deriving bounds on the shape parameters of the weak and electromagnetic form factors using as input correlators calculated from perturbative QCD, and exploiting analyticity and unitarity. The values resulting from the symmetries of QCD at low energies or from lattice calculations at special points inside the analyticity domain can beincluded in an exact way. We write down the general solution of the corresponding Meiman problem for an arbitrary number of interior constraints and the integral equations that allow one to include the phase of the form factor along a part of the unitarity cut. A formalism that includes the phase and some information on the modulus along a part of the cut is also given. For illustration we present constraints on the slope and curvature of the K_l3 scalar form factor and discuss our findings in some detail. The techniques are useful for checking the consistency of various inputs and for controlling the parameterizations of the form factors entering precision predictions in flavor physics.Comment: 11 pages latex using EPJ style files, 5 figures; v2 is version accepted by EPJA in Tools section; sentences and figures improve

Analyticity, Shapes of Semileptonic Form Factors, and B to pi l nu

We give a pedagogical discussion of the physics underlying dispersion relation-derived parameterizations of form factors describing B -> pi l nu and B -> D l nu. Moments of the dispersion relations are shown to provide substantially tighter constraints on the f_+ (t) form factor describing B -> pi l nu than the unweighted dispersion relation alone. Heavy quark spin symmetry relations between the B -> pi l nu and B^* -> pi l nu form factors enables such constraints to be tightened even further.Comment: 18 pages, Latex, three eps figures include

Usable Science for Managing Animals and Rangeland Sustainability

On the Ground: • Animals are critical components of rangeland ecosystems, and domestic livestock provide an extremely important management tool on rangelands. • Decades of research have yielded much valuable information to support sustainable and effective grazing management, but increased complexity resulting in part from expanding environmental, economic, and societal pressures demands future investments in usable science focused on rangeland animals. • Three priorities for usable science are recommended: • Proactive drought planning • Better matching livestock production systems to rangeland resources • Comprehensive synthesis of and effective communication concerning environmental impacts (positive, negative, and neutral) of livestock on rangelands.The Rangelands archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform March 202