Comparison of the primary structures of the SRLV and HIV-1 Vpr and Tat proteins. The putative domains of MVV Tat, HIV-1 Tat, and HIV-1 Vpr are shown as stained boxes. The HIV-1 Tat protein contains an N-terminal proline-rich domain (Pro), a cysteine-rich domain (Cys), a core, a basic domain (basic), and a glutamine-rich domain (Gln). The HIV-1 Vpr protein contains an N-terminal acidic domain (acidic), two leucine-rich domains (Leu), and a basic domain (basic). MVV Tat protein contains an N-terminal acidic domain (acidic), a leucine-rich domain, and a cysteine-rich domain.