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Plant viruses have been instrumental in our understanding of the biophysical properties pertaining to non-enveloped icosahedral virus particles. A substantial amount of research has been performed over five decades on Turnip yellow mosaic virus (TYMV), arguably one of the most extensively studied icosahedral plant viruses and the type-member of the Tymovirus plant virus genus. Even with a substantial body of published scientific literature, little is known about the role of specific coat protein (CP) residues in TYMV assembly, disassembly and disencapsidation. We have shown through our mutagenesis studies that the N-terminal region of the CP that is involved in the formation of an annulus structure and is disordered in A-subunit pentamers is not essential in vivo, but annulus-forming residues are critical in ensuring virion stability and low accessibility after virus is purified (Chapter 2). We have shown that a range of amino acid residue types is tolerated within the CP N-terminus in vivo, although they can greatly affect the stability of virions and empty particles, most notably at low pH (Chapter 3). Unlike full-length CP, N-terminal deletion and substitution mutants fail to reassemble into particles in vitro (Chapter 2, 3) suggesting a critical determinant for the N-terminus in reassembly (discussed Chapter 7). This is the first documented in vitro reassembly reported for a member of the Tymoviridae family and should provide a framework for further studies. We have identified a new way to create empty artificial top component (ATC)-particles through treatment with EDTA (Chapter 6) and we also show that tymoviruses can be engineered with altered pH-dependent enhanced stability (Chapter 4). In collaboration with the Qian Wang laboratory from the University of South Carolina we have shown that an RGD (Arg-Gly-Asp) motif can be genetically engineered within the CP of TYMV, resulting in infectious particles with attractive stem-cell adhesion properties (Chapter 5). With focus on basic viral mechanisms, we have crystallized the TYMV virion and ATC particle at pH 7.7 and collected data to less than 5 Å resolution (Chapter 4, supplementary). These structures represent the first tymovirus-based structures solved above pH 5.5 and will provide insight into the N-terminal conformations within the TYMV particle. Finally, we have characterized an N-terminal CP cleavage seen after ATC formation (Chapter 4) suggesting an additional and yet uncharacterized feature associated with decapsidation. / Graduation date: 2012