HIV-1 protease mediates virus maturation by processing viral structural protein Gag precursors during or after virus budding. The PR-mediated virus maturation is necessary for acquisition of viral infectivity. Timing of PR activation appears to be critical for virus assembly as premature PR activation can reduce virion release due to premature cleavage of Gag. Our primary goal is to elucidate the mechanism of PR activation. We also analyze the SARS-CoV structural domains involved in virus particle assembly. BST-2/tetherin has been reported to restrict enveloped virus release by tethering the progeny virions to the cell surface. We investigate the impact of BST-2/tetherin on coronavirus replication and explore whether coronaviruses or SARS-CoV has not yet identified strategy to oppose the BST-2/tetehrin anti-viral function.