| The Flp recombinase is a member of the lambda-integrase family of site-specific recombinases. During its catalytic cycle, it exhibits half-of-the-sites activity, a feature that is conserved throughout the lambda-integrase family, although the Flp recombinase is unique in that it assembles each active site in trans. In the first two chapters, a tetramer of a mutant of the Flp protein bound to a Holliday junction intermediate is discussed. Substantial rigid body motion, in comparison with the previously determined Flp structure, is seen within the tetramer. These motions highlight differences in flexibility between the two types of protein-protein interfaces and better define the range of conformations available to the catalytically active tetramer. From these results a model implicating steric occlusion in the enforcement of half-of-the-sites activity is proposed.; Rad51, the major eukaryotic homologous recombinase, is important for the repair of double strand breaks. The active form of this DNA-dependent ATPase is a helical filament within which the search for homology and strand exchange occurs. Chapters three and four discuss a crystal structure of the S. cerevisiae Rad51 filament, showing the ATPase site directly at the interface between protomers. While crystals used for the determination of this structure were grown in the presence of ssDNA, no DNA is observed in the filament. The filament has a pitch of 129A and displays approximate 6, symmetry, with alternate protein-protein interfaces are slightly different, implying that the functional unit of Rad51 within the filament may be a dimer. |
