The kinase activity of P-TEFb is inhibited when the factor is in the 7SK snRNP. P-TEFb can be released from the 7SK snRNP by either the HIV transactivator Tat or the bromodomain containing protein BRD4. This release leads to a conformational change in 7SK RNA and the ejection of HEXIM.
The activity of P-TEFb is suppressed when it interacts with the 7SK snRNP. However, P-TEFb can be released from this interaction by either Tat or BRD4, resulting in a structural rearrangement of 7SK RNA and the expulsion of HEXIM.