Protein Domain : Hepatitis delta antigen (HDAg) domain IPR037517

Type	Domain
Description	Transcription elongation by RNA polymerase II (RNAPII) is negatively regulated by the human factors DRB-sensitivity inducing factor (DSIF) and negativeelongation factor (NELF). NELF is a transcription factor composed of four subunits, NELF-A, -B, -C (or its variant -D), and -E, that are conserved fromDrosophila to humans. Certain subunits have been implicated in numerous diseases ranging from neurological disorders to cancer. The N-terminal segmentof NELF-A shows sequence similarity to the hepatitis delta antigen (HDAg), the viral protein required for replication of hepatitis delta virus (HDV) [E1]. Replication of HDV RNA appears to involve the host RNAPII and requires thepresence of HDAg. HDAg binds RNAPII directly and stimulates transcription by displacing NELF and promoting RNAPII elongation. HDAg directly binds RNAPIIand inhibits NELF-RNAPII association, possibly because HDAg competes with NELF-A for a common surface on RNAPII [, ].The C terminus of the HDAg domain forms the RNAPII-binding motif conserved in humans and virus, while the NELF-C (or NELF-D)-binding region of NELF-A islocalized in the middle of the HDAg domain. The region of HDAg corresponding to the NELF-C (or NELF-D)-binding region of NELF-A contains two arginine-richmotifs responsible for RNA-binding activity [ , , ].The HDAg domain is composed of a long N-terminal helix, interrupted by a sharp bend and continuing on into another short helix [ , ]. Themiddle part of the HDAg domain makes an 'extended region' that forms four helices []. The structure of the C-terminal section is notyet known.
Short Name	HDAG_dom