PHF3 is a human homolog of yeast protein bypass of Ess1 (Bye1), a nuclear protein with a domain resembling the central domain in the transcription elongation factor TFIIS. It is ubiquitously expressed in normal tissues including brain, but its expression is significantly reduced or lost in glioblastomas. PHF3 contains an N-terminal plant homeodomain (PHD) finger, a central RNA polymerase II (Pol II)-binding TFIIS-like domain (TLD) domain, and a C-terminal Spen paralogue and orthologue C-terminal (SPOC) domain.