ABSTRACT This Core provides peptide, protein, antibody and RNA reagents that support HIV/Host structural and mechanistic studies within the CHEETAH Center. Bacterial expression systems will be the workhorse for producing recombinant proteins without complex folding/post-translational modification requirements, while eukaryotic expression systems will be employed to produce more complex proteins. Uniformly glycosylated or deglycosylated proteins will be made using advanced tissue culture and enzymatic approaches.1-3 Membrane proteins will be produced by coupling eukaryotic expression with comprehensive detergent screening protocols.4 Peptide synthesis will be employed for the production of ligands, inhibitors, and protein fragments. Larger synthetic peptides/proteins will be produced using native chemical ligation to enable the introduction of site-specific labels and modifications.5 Finally, an automated high-throughput phage display screening and characterization platform will be used to produce Fab antibody fragments for use as crystallography chaperones, cryo-EM fiducials, biochemistry/cell biology tools, and to stabilize/trap heterogeneous protein complexes in specific conformations for structural studies.6