Prolyl isomerase Pin1 shares functional similarity with phosphorylated CTD interacting factor PCIF1 in vertebrate cells.

The carboxy-terminal domain (CTD) of the RNA polymerase II (Pol II) largest subunit undergoes reversible phosphorylation during transcription cycle. The phosphorylated CTD plays critical roles in coordinating transcription with chromatin modification and RNA processing by serving as a scaffold to recruit various proteins. Recently, we identified a novel human WW domain-containing protein PCIF1 as a phosphorylated CTD-interacting factor and demonstrated that PCIF1 negatively modulates Pol II activity in vivo.

Human phosphorylated CTD-interacting protein, PCIF1, negatively modulates gene expression by RNA polymerase II.

Phosphorylation of the C-terminal domain (CTD) of the largest subunit of RNA polymerase II (Pol II) regulates transcription cycle and coordinates recruitment of RNA processing factors and chromatin regulators. Recently, we reported the identification of human PCIF1 as a novel protein that directly binds to the phosphorylated CTD via its WW domain, which is highly homologous to the WW domain of human peptidylprolyl isomerase Pin1. Although PCIF1 has been shown to associate with phosphorylated Pol II, functional consequence of the interaction remains unclear.