Transcription factor that binds RNA polymerase II and inhibits the elongation of transcripts from target promoters. Regulates transcription elongation in a TATA box-dependent manner (By similarity). Binds RNA polymerase II, HD and SF1 (By similarity). Binds formin. Interacts (via the second WW domain) with TREX1 (via proline-rich region). The FF domains preferentially binds peptides with the consensus sequence [DE](2-5)-[FWY]-[DE](2-5) and mediate interaction with HTATSF1 and probably bind the phosphorylated C-terminus of the largest subunit of RNA polymerase II. The WW domains bind Pro-rich domains.