Figure 1. Release of P-TEFb from the 7SK snRNP by HIV Tat.

A) P-TEFb release reactions were performed as described in Materials and Methods. Indicated amounts of Tat were incubated for the indicated times with immunoprecipitated 7SK snRNPs. B) Same as in A except the RNA binding deficient mutant of Tat (Tat R52/53A) was used. C) Same as in A except the P-TEFb binding deficient mutant of Tat (Tat C22G) was used. D) Tat release was quantified from three independent experiments for wild type Tat and the RNA binding mutant and two independent experiments for the P-TEFb binding mutant. Mean values for the percent of Cdk9 left in the complex are plotted and all error bars represent standard error. E) 100 ng of Tat was incubated with the indicated amounts of TAR or 7SK RNA before being added to the 7SK snRNP. F) Same as in E except TatR52/53A was used.