To test whether the knock-down of cyclin T1 in MM6 cells inhibits the cyclin T1/P-TEFb complex and therefore Tat function in vivo, infections were carried out with two HIV-1 luciferase reporter viruses: a virus expressing a wild-type Tat protein and a mutant virus that expresses a non-functional Tat protein. Here, CCNT1 is linked to infection.