CDK9 kinase activity does not require S175.

Abstract

<p>Radioactive <i>in vitro</i> kinase assays perfomed using FLAG-CDK9 complexes isolated from Jurkat 2D10 cells stimulated for 20 h with 10 ng/mL TNF-α to induce Tat expression. Western blots of these IPs and the corresponding WCEs are shown in the lower panel of <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003338#ppat-1003338-g005" target="_blank"><b>Fig. 5B</b></a>. The kinase assays were performed in the absence (A) or presence (B) of 250 ng of His-tagged full length human pol II CTD repeat substrate. Inhibition of activity by pretreatment with 100 nM flavopiridol confirms the activity in both assays to be CDK9 kinase. Note that the S175A and S175D mutations display wildtype kinase activity in both assays.</p