CDK9 phosphorylated at Ser175 is excluded from the 7SK snRNP complex.

Abstract

<p>2D10 cells were engineered to stably express FLAG-HEXIM1. Left panels: WCEs were prepared from cells that were unstimulated or treated with PMA for 1 h with or without the inhibitor U0126. Right panels: FLAG-HEXIM1 complexes were isolated by anti-FLAG IP followed by elution with FLAG peptide. Immunoblotting was performed on whole cell extracts (input samples) and anti-FLAG immunoprecipitates using antibodies towards CycT1, CDK9, HEXIM1, LARP7, pT186 CDK9, and pSer175 CDK9. The result shown is representative of two different experiments. Note that HEXIM1- P-TEFb found in the HEXIM-associated complexes is devoid of phosphorylation at Ser175 whereas the modification is readily detected in WCEs and in FLAG-CDK9 immunoprecipates (<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003338#ppat-1003338-g003" target="_blank"><b>Fig. 3</b></a>).</p