The impact of mutations in the Gag-Pol polyprotein on protease activity. The letters above the diagram indicate cleavage sites; cleavage at sites E and F release the protease; subsequent cleavage at sites C, A, and B produce mature structural proteins. Regions in Gag that impact protease processing have been defined by deletion analysis (underlined). Specific mutations (indicated by dots), particularly at the sites between nucleocapsid (p7NC)and p6 or p6* (depending on the reading frame), can alter the rates of protease processing at different cleavage sites (green circles: our unpublished data; black circles: summary of published data.) For abbreviations see Figure 5.