FIG. 3.
Squelching assays revealed functional interactions between CDK9 and cyclin T1 in cells. The expression of free CDK9 reduced effects of the hybrid RevCDK9 protein on SLIIB (15- to 3-fold transactivation [lanes 2 and 3, white and cross-hatched bars]). However, the coexpression of increasing amounts of cyclin T1 together with CDK9 and the chimera restored levels of transactivation from 8- to 15-fold (lanes 4 to 6, cross-hatched bars). The coexpression of Tat had limited effects on the hybrid RevCDK9 protein (16-fold to 10-fold transactivation [lanes 7 and 8, black bars]). A total of 0.1 μg of the plasmid effector was used. Amounts of plasmid effectors are given below the bar graph. The introduction of various proteins had minimal effects on the expression of LacZ from the cotransfected pCMVβGal, which served as our internal control plasmid (table; expressed as absorbance units). Experiments are representative of two independent transfections performed in duplicate where the standard errors of the means are given. OD450, optical density at 450 nm.