Disruptions of the Ustilago maydis REC2 gene identify a protein domain important in directing recombinational repair of DNA

The REC2 gene of Ustilago maydis encodes a homologue of the Escherichia coli RecA protein and was first identified in a screen for UV-sensitive mutants. The original isolate, rec2-1, was found to be deficient in repair of DNA damage, genetic recombination and meiosis. We report here that the rec2-197 allele, which was constructed by gene disruption, retains some biological activity and is partially dominant with respect to REC2. The basis for the residual activity is probably as a result of expression of a diffusible product from the rec2-197 allele that augments or interferes with REC2 functions. This product appears to be a polypeptide expressed from a remnant of the 5' end of the open reading frame that was not removed in creating the gene disruption. The mutator activity and disturbed meiosis of rec2-197 suggest that the Rec2 protein functions in a process that avoids spontaneous mutation and insures faithful meiotic chromosome segregation. A prediction based on the phenotype of rec2-197 is that Rec2 protein interacts with one or more other proteins in directing these functions. To identify interacting proteins we performed a yeast two-hybrid screen and found Rad51 as a candidate. Rec2-197 and Rad51 appear to interact to a similar degree

Local anharmonic vibrations strong correlations and superconductivity: A quantum simulation study

We investigate the importance of local anharmonic vibrations of the bridging oxygen in the copper oxide high-T c materials in the context of superconductivity. For the numerical simulation we employ the projector quantum Monte Carlo method to study the ground state properties of the coupled electron-phonon system. The quantum Monte Carlo simulation allows an accurate treatment of electronic interactions which investigates the influence of strong correlations on superconductivity mediated by additional quantum degrees of freedom. As a generic model for such a system, we study the two-dimensional single band Hubbard model coupled to local pseudo spins (bridging oxygen), which mediate an effective attractive electron-electron interaction leading to superconductivity. The results are compared to those of an effective negativeU model