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Nod, a nonmotile kinesin-like protein, plays a critical role in segregating achiasmate chromosomes during female meiosis. In addition to localizing to oocyte chromosomes, we show that functional full-length Nod-GFP (Nod(FL)-GFP) localizes to the posterior pole of the oocyte at stages 9-10A, as does kinesin heavy chain (KHC), a plus end-directed motor. This posterior localization is abolished in grk mutants that no longer maintain the microtubule (MT) gradient in the oocyte. To test the hypothesis that Nod binds to the plus ends of MTs, we expressed and purified both full-length Nod (Nod(FL)) and a truncated form of Nod containing only the motor-like domain (Nod318) from Escherichia coli and assessed their interactions with MTs in vitro. Both Nod(FL) and Nod318 demonstrate preferential binding to the ends of the MTs, displaying a strong preference for binding to the plus ends. When Nod318-GFP:MT collision complexes were trapped by glutaraldehyde fixation, the preference for binding to plus ends versus minus ends was 17:1. Nod(FL) and Nod318 also promote MT polymerization in vitro in a time-dependent manner. The observation that Nod is preferentially localized to the plus ends of MTs and stimulates MT polymerization suggests a mechanism for its function.

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The potential energy hypersurface for H2P(OH)2 has been explored at correlated levels. Seven local minima and 29 different stereopermutational transition states interconnecting them were located. The transition states correspond to internal rotation, pseudorotation, double pseudorotation, and pseudoinversion. The stereochemical consequences of these processes are analyzed in detail as is the nature of the singly occupied molecular orbital throughout. Geometric and natural bond orbital analyses indicate the importance of hyperconjugative interactions through phosphorus in stabilizing various kinds of stationary points. The latter effect is maximized for the interaction of equatorial substituents in the trigonal-bipyramidal phosphoranyl minima. Comparison to closed shell phosphoranes and monohydroxy-and other phosphoranyl radicals is provided. Dihydroxyphosphoranyl is predicted to possibly be stable to homolytic decomposition under suitable conditions and calculated electron spin resonance and infrared spectral data are provided.

The potential energy hypersurfaces for HnP(OH)4-, and HnP(OCH3)4-n3 n = 0 or 1, have been explored at correlated levels using polarized valence double-5 and triple-5 basis sets. Numerous local minima and several distinct types of stereopemutational transition states interconnecting them have been identified. These transition states correspond to (i) bond rotation, (ii) pseudorotation, (iii) double pseudorotation, and (iv) pseudoinversion.The stereochemical consequences of these processes are analyzed in detail as is the nature of the singly occupied molecular orbital throughout. Geometric and natural bond orbital analyses indicate the importance of stabilizing hyperconjugative interactions in these systems. The latter effect is maximized for interactions between equatorial substituents in trigonal bipyramidal (TBP) phosphoranyl structures. Unlike the TBP local minima of the mono-and dihydroxyphosphoranyls, where the unpaired electron always localizes in an equatorial site, tri-and tetrahydroxyphosphoranyl minima localize their unpaired electrons in both equatorial and apical positions.