FIG. 1. (facing page). Activation and function of the positive transcription elongation factor-b (P-TEFb) (cyclin T/Cdk9) in cardiac muscle hypertrophy. (Upper panel) Schematic representation of the RNA polymerase II (RNAPII) phosphorylation-dephosphorylation cycle and its modulation by physiological, pharmacological, and genetic triggers of hypertrophy. Upstream signals (a) and direct manipulations of Cdk9 activity (b-d) correspond to data illustrated in the lower panels. [Reproduced and modified from Sano M, Abdellatif M, Oh H, Xie M, Bagella L, Giordano A, Michael LH, DeMayo FJ, Schneider MD 2002 Activation and function of cyclin T-Cdk9 (positive transcription elongation factor-b) in cardiac muscle-cell hypertrophy. Nature Med 8:1310–1317, with permission of the Nature Publishing Group.]