Project Summary/Abstract This proposal describes a four year career development plan and a research strategy for Dr. Robert Orchard to transition from a postdoctoral fellow to an independent academic faculty position investigating host- pathogen interactions. The mentored phase of the award (K99) will be completed under the continued guidance of Dr. Herbert `Skip' Virgin in the Department of Pathology and Immunology at Washington University School of Medicine. The overall research goal of the proposal is to determine molecular mechanisms of norovirus cofactors upon viral entry. Candidate: I have a long standing interest in understanding the molecular mechanisms underlying complex host-pathogen interactions. I graduated summa cum laude from Texas A&M University with a degree in Microbiology. I subsequently joined the Molecular Microbiology Graduate Program at University of Texas Southwestern Medical School. For my doctoral thesis in Dr. Neal Alto's laboratory, I described how bacterial virulence proteins usurp the host cytoskeletal machinery and engineer pathogenic-signaling circuits within the complex environment of the cytoplasm of eukaryotic host cells. I then began a postdoctoral fellowship under the mentorship of Dr. Skip Virgin. During my fellowship in Dr. Virgin's lab, it has been my goal to couple my experiences with dissecting host-pathogen signaling networks with his ability to define the in vivo relevance of host-pathogen interactions in animal models. To this end, my research project has been focused on understanding the molecular mechanisms of murine norovirus (MNoV) replication and tropism due to its robust in vitro and in vivo systems. Specifically, we recently completed a whole-genome CRISPR screen for host genes required for MNoV replication. We discovered that MNoV binds a proteinaceous receptor, CD300lf, that is necessary both in vitro and in vivo for MNoV replication and when expressed in human cells sufficient to break the species barrier of MNoV replication. Additionally, our work described a novel, unidentified cofactor in serum required for efficient MNoV binding to cells. This work is the foundation for the research proposal outlined here. I plan to focus the remainder of my fellowship on obtaining professional skills and scientific insight necessary to transition to a tenure-track position. Career Development Plan: During my final year as a postdoctoral fellow, I will focus a significant amount of effort (15%) to developing the professional skills challenging to me that are necessary for successful independent investigators. I have assembled a career advisory committee composed of Dr. Daved Fremont, Dr. Michael Diamond, and Dr. Thaddeus Stappenbeck that will evaluate my progress in overcoming deficiencies in scientific writing and data presentation, mentoring, and laboratory management along with my scientific progress. Additionally, I will attend specific seminars both within and outside of Washington University to en...