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. Septins are GTP-binding proteins encoded by paralogous genes found in the genomes of nearly every eukaryote examined. These proteins are involved in the remodeling of and demarcation of compartments within the plasma membrane, for example during cytokinesis (Finger, 2005) and in the maturation of dendritic spines in neurons (Caudron and Barral, 2009). Unicellular eukaryote Saccharomyces cerevisiae (baker's yeast) encodes seven septin genes, and Homo sapiens fourteen (Pan et al., 2007). Any given eukaryotic cell type expresses multiple sets of septins, often in a cell type- and developmental stage-specific manner. In all cases known, the protein products of those genes associate in a defined order and assemble into a linear array (McMurray and Thorner, 2008a; Weirich et al., 2008). Moreover, the resulting linear hetero-oligomer ("rod") is a building block that has the capacity to undergo end-on-end polymerization, thereby forming filaments. It is known that these filaments are involved with cell division, but fluorescence microscopy alone has not revealed sufficient details to thoroughly understand the exact mechanism. We propose to use correlated fluorescence and x-ray imaging to determine the location of each of the septins in the yeast, Saccharomyces cerevisiae.