TCEAL1 (transcription elongation factor A (SII) protein 3), also known as p21, SIIR or pp21, is a member of the TFS-II family. Transcription elongation factors of the TFS-II family are responsible for releasing RNA polymerase II (Pol II) from transcriptional arrest. DNA arresting sites can result in locked ternary complexes if elongating RNA polymerases are trapped. Transcription elongation factors function to activate the intrinsic RNA cleavage activity of RNA polymerases. This allows the RNA polymerase to cleave the nascent transcript, thereby forming a new 3’-terminus to resume elongation. TCEAL1 is a 157 amino acid nuclear protein that is ubiquitously expressed. TCEAL1 may exert its effects via protein-protein interactions with other transcriptional regulators rather than via direct binding of DNA.