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. Author manuscript; available in PMC: 2013 Jan 1.
Published in final edited form as: Wiley Interdiscip Rev RNA. 2011 Aug 18;3(1):92–103. doi: 10.1002/wrna.106

Figure 2. Reversible association of P-TEFb and HEXIM with the 7SK snRNP.

Figure 2

Cyclic model for interactions between P-TEFb and the 7SK snRNP. Left: The 7SK snRNP containing the indicated proteins is acted upon directly by Tat and Brd4,36 or by UV light, actinomycin D, any P-TEFb inhibitor, HMBA, or SAHA (release). P-TEFb is extracted from the snRNP, which causes the subsequent release of HEXIM. Right: After release of P-TEFb and HEXIM, there is a conformational change in the RNA that is stabilized by hnRNPs. LARP7 and MePCE remain associated with 7SK snRNA. The release of P-TEFb and HEXIM is not directly reversible and the mechanism involved in re-sequestration of HEXIM and then P-TEFb remains unknown.