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. 2007 Mar 6;35(6):2003–2012. doi: 10.1093/nar/gkm063

Figure 4.

Figure 4.

Tat disrupts the endogenous 7SK snRNP to release P-TEFb. (A) NEs prepared from HeLa cells either untransfected (−) or transfected with the indicated plasmids (20 µg per 15–cm dish) encoding wild-type or mutant Tat-F proteins were subjected to anti-Cdk9 or, as a negative control, anti-Cdk4 immunoprecipitation. The levels of endogenous 7SK, CycT1 and HEXIM1 bound to Cdk9 as revealed by northern or western blotting are indicated (bottom panels). The upper panels show the levels of the endogenous 7SK, CycT1, HEXIM1 and Cdk9 as well as the various transfected Tat-F proteins in HeLa NEs. (B) NEs prepared from HeLa cells transfected with an empty vector (−) or the Tat-F-encoding plasmid (20 µg/15-cm dish) were subjected to glycerol gradient sedimentation analysis. The panels show the western detection of CycT1, HEXIM1 and Cdk9 in gradient fractions (left). Molecular size standards were analyzed in a parallel gradient and their positions indicated by arrows.