HIP1 and HIV-1 infection: If the interaction is essential for efficient Vpr-induced G2 arrest and HIV-1 infection in macrophages, whether Vpr interacts with HIP1 directly or indirectly, whether the interaction between Vpr and HIP1 alters the structure of Vpr, whether HIP1 affects the binding of Vpr to other host proteins via the interaction, and which domains of Vpr and HIP1 mediate the interaction remain to be determined.