Fig 2: siRNA-based Cdc42 knockdown modulated the CTD phosphorylation code and affected the level of CTD phosphatases and kinases in HeLa cells. (A) HeLa cells 48 hr after Cdc42 siRNA transfection. (B) Western blot showing the levels of Cdc42, Ser2P, Ser5P, Ser7P and CTD phosphatases (FCP1 and RPAP2) and kinases (CDK7 and CDK13) in Cdc42 siRNA-transfected HeLa cells. Tubulin was used as the protein loading control. Quantitative analysis of the Western blot results from two independent biological replicates was shown. Protein level in the control was set as 1.0. Significance level is indicated by * (p < 0.05) or ** (p < 0.01) vs. control. The letter a above the column indicates a marginal difference (p = 0.058) compared to control.

Fig 3: A hypothetical model for the Rho-Pol II signaling shortcut in transcriptional control in cultured human cells. Once activated by extracellular signals, Rac1 and Cdc42 GTPases positively control the degradation of CTD kinases (CDK7 and CDK13) but negatively and differentially control the degradation of CTD phosphatases (FCP1 for Rac1 and RPAP2 for Cdc42) in modulation of the Pol II CTD code (Ser2P and Ser5P). Feedback regulation of DOCK4 and DOCK9, the activators of Rac1 and Cdc42, respectively, is hypothesized to be achieved by transcriptional control of these DOCK genes (indicated by dotted green arrows).