This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Our lab is interested in understanding proteins involved in cellular DNA transactions. Specifically, we attempt to elucidate the mechanisms that allow for efficient transfer of DNA repair/replication intermediates to subsequent binding partners through the use of structural biology techniques such as NMR, X-ray crystallography and small-angle X-ray scattering. Small-angle X-ray scattering experiments carried out at the Bio-CAT beamline were intended to examine a series of protein:protein and protein:DNA complexes that are involved in repairing damaged DNA. The one day of beamtime that was allocated through the entire cycle of the grant allowed us to carry out our initial characterization of these complexes;additional experiments are planned to follow up on our preliminary results, with allocation of beamtime being the limiting factor. Aside from our project on DNA repair, SAXS data was collected on a DNA endonuclease that is involved in pneumonia infections. These data resulted in a single publication describing our biochemical and biophysical analysis of this protein. The SAXS data collected at Bio-CAT allowed for determination of stoichiometry of this protein, which was previously debated, as other members of this family are known to dimerize. Additionally, ab-initio models were generated that allowed for comparison of the SAXS-based envelope model with homologous crystal structures.