The stimulatory effects of several DNA-binding basic proteins (histone and protamine) and HIV-1 Rev with arginine (Arg)-rich clusters on the activity of casein kinase II (CK-II) were investigated in vitro. It was found that recombinant Rev (rRev) and the synthetic oligo-fragments corresponding to the amino acid sequences of its Arg-rich cluster stimulate CK-II activity in a dose-dependent manner. The activated CK-II phosphorylates several cellular and viral proteins in HIV-1 infected human MOLT-4 cells, and also phosphorylates HIV-1 structural proteins, including recombinant reverse transcriptase (rRT). These phosphorylations are selectively inhibited by CK-II inhibitors, such as quercetin, oGA (a glycyrrhetinic acid derivative) and NCS-chrom (an enediyne containing antibiotic). The data presented here suggest that HIV-1 Rev acts as an effective potent activator of CK-II, which may be a cellular mediator promoting HIV-1 replication in virus-infected cells.