Expression of NIPP1 inhibits Tat-dependent HIV-1 transcription in COS-7 cells. A, Lane 1, COS-7 cells grown in 24-well plate were transfected with the indicated amount of JK2 using Ca2+-phosphatase method. Lane 2, COS-7 cells were transfected with 25 ng of JK2 and indicated amount of Tat expression plasmid. Lane 3 and 4, COS-7 cells were transfected with 25 ng of JK2, 50 ng of Tat expression vector and indicated amounts of wild type or mutant NIPP1. B, NIPP1 and mutant NIPP1 equally affect HIV-1 transcription in the absence of Tat. COS-7 cells were transfected with 50 ng of JK2 or JK2ΔTAR and with indicated amounts of NIPP1 or mutant NIPP1.