Involvement of phosphatidylinositol 4,5-bisphosphate in RNA polymerase I transcription.

RNA polymerase I (Pol I) transcription is essential for the cell cycle, growth and protein synthesis in eukaryotes. In the present study, we found that phosphatidylinositol 4,5-bisphosphate (PIP2) is a part of the protein complex on the active ribosomal promoter during transcription. PIP2 makes a complex with Pol I and the Pol I transcription factor UBF in the nucleolus. PIP2 depletion reduces Pol I transcription, which can be rescued by the addition of exogenous PIP2. In addition, PIP2 also binds directly to the pre-rRNA processing factor fibrillarin (Fib), and co-localizes with nascent transcripts in the nucleolus. PIP2 binding to UBF and Fib modulates their binding to DNA and RNA, respectively. In conclusion, PIP2 interacts with a subset of Pol I transcription machinery, and promotes Pol I transcription.