Anti-FCP1 (aa 1-100) polyclonal antibody

The elongation phase of eukaryotic transcription by RNA polymerase II (RNAPII) is an important target for regulation of gene expression. An interplay of positive and negative elongation factors determines the elongation activity of RNAPII in different promoters. The phosphorylation status of the carboxyl-terminal-domain (CTD) of the larger subunit of RNAPII appears to be the regulatory focus of different factors regulating mRNA processivity. The emerging model of the transcription cycle proposes that the phosphorylation state of the CTD is dynamic during elongation with different forms predominating at different stages of transcription. Shortly after initiation RNA polymerase II comes under the control of negative elongation factors and enters abortive elongation. Escape from the action of these negative controls requires the action of at least one positive elongation factor identified in the P-TEFb complex composed of the Cyclin-Dependent Kinase CDK9 and its regulatory subunit cyclin T. Finally, the requirement of CTD phosphatase activity, identified in the FCP1 protein, has been invoked as necessary to recycle the hypophosphorylated form of the RNA polymerase II competent to reinitiate the transcription cycle.

The C-terminal domain of the RNA polymerase (RNAP) 11 largest subunit (CTD) plays critical roles both in transcription of mRNA precursors and in the processing reactions needed to form mature mRNAs. The CTD undergoes dynamic changes in phosphorylation during the transcription cycle, and this plays a significant role in coordinating its multiple activities. But how these changes themselves are regulated is not well understood. Here we show that the peptidyl-prolyl isomerase Pin1 influences the phosphorylation status of the CTD in vitro by inhibiting the CTD phosphatase FCP1 and stimulating CTD phosphorylation by cdc2/cyclin B. This is reflected in vivo by accumulation of hypophosphorylated RNAP 11 in pin1(-/-) cells, and of a novel hyper-hyperphosphorylated form in cells induced to overexpress Pin1. This hyper-hyperphosphorylated form of RNAP 11 also accumulates in M-phase cells, in a Pin1-dependent manner, and associates specifically with Pin1. Functionally, we find that Pin1 overexpression specifically inhibits ongoing transcription of mRNA precursors in vivo and both transcription and RNAP II-stimulated pre-mRNA splicing in cell extracts. Pin1 thus plays a significant role in regulating RNAP 11 CTD structure and function.