Figure 3. Schematic of CLP-1 control of P-TEFb and gene transcription. When CLP-1 is bound to P-TEFb, the cdk9 kinase is inhibited and RNA pol II remains in an initiation state in which “paused” RNA synthesis produces only nascent RNAs. Dissociating or preventing CLP-1 from binding to P-TEFb de-represses cdk9 to phosphorylate RNA pol II and activate it to an elongation state in which it completes nascent RNA transcripts. The association of CLP-1 with P-TEFb is reversible and potentially subject to control by other factors such as signal transducers or transcription factors in their effort to promote transcription of their target genes.