The Core Project consists of two sub-projects, both of which support the objectives of the other Projects within the Program as a whole. In Project F1 we propose to acquire test-image data-sets for ice-embedded single particles, which will be archived in a way that is available simultaneously to the software developers in this program project and to the community via the web. The known atomic structures of these specimens will provide a reality check for validating our computational methodology. The broader availability of the data sets should further stimulate new algorithmic development towards atomic structure determination by electron cryomicroscopy of single particles. Our primary test molecules will be GroEL particles and tubulin (in the form of microtubules), both of which are chosen because of their known atomic structure, appropriate size and inherent symmetry. We will obtain focal pairs of images for more than 300,000 single-particles of each type of sample. Images will be recorded on the JEOL3000 field emission electron cryo-microscopes (equipped with a liquid helium cryo-stage) located in Houston and in Berkeley. in addition to the labor-intensive data recording, we expect to be involved in improving the methodology of specimen preparation and efficient data-recording. Project F2 will provide key scientific infrastructure that is needed within the Program. Project F2 will also provide local scientific expertise in cryo-EM that is needed to support the work of Projects C and D, for which the primary expertise of the PIs lies in computer science and mathematics, respectively. Finally, Project F2 will coordinate a range of centralized functions that are related to efficient communication and collaboration between all Projects.