HB1/Asxl, restriction endonuclease HTH domain (IPR007759)

Short name: HB1/Asxl_HTH

Overlapping homologous superfamilies

Domain relationships



This entry represents a winged helix-turn-helix domain present in the plant HB1, vertebrate ASXL, the H. pylori restriction endonuclease HpyAIII(HgrA), the RNA polymerase delta subunit(RpoE) of Gram positive bacteria and several restriction endonucleases [PMID: 10336502]. The domain is distinguished by the presence of a conserved one-turn helix between helix-3 and the preceding conserved turn. Its diverse architectures in eukaryotic species with extensive gene body methylation is suggestive of a chromatin function. The genetic interaction of the HARE-HTH containing ASXL with the methyl cytosine hydroxylating Tet2 protein is suggestive of a role for the domain in discriminating sequences with DNA modifications such as hmC [PMID: 10336502]. Bacterial versions include fusions to diverse restriction endonucleases, and a DNA glycosylase where it may play a similar role in detecting modified DNA. Certain bacterial version of the HARE-HTH domain show fusions to the helix-hairpin-helix domain of the RNA polymerase alpha subunit and the HTH domains found in regions 3 and 4 of the sigma factors [PMID: 10336502]. These versions are predicted to function as a novel inhibitor of the binding of RNA polymerase to transcription start sites, similar to the Bacillus delta protein [PMID: 7545758, PMID: 22186017].

The delta protein is a dispensable subunit of Bacillus subtilis RNA polymerase (RNAP) that has major effects on the biochemical properties of the purified enzyme. In the presence of delta, RNAP displays an increased specificity of transcription, a decreased affinity for nucleic acids, and an increased efficiency of RNA synthesis because of enhanced recycling [PMID: 10336502]. The delta protein, contains two distinct regions, an N-terminal domain and a glutamate and aspartate residue-rich C-terminal region [PMID: 7545758]. It participates in both the initiation and recycling phases of transcription.

The Asx-like (Asxl) proteins includes Asxl1-3. They are putative Polycomb group (PcG) proteins, which act by forming multiprotein complexes that are required to maintain the transcriptionally repressive state of homeotic genes throughout development. Asxl1 is involved in transcriptional regulation mediated by ligand-bound retinoic acid receptors (RARs) and peroxisome proliferator-activated receptor gamma (PPARG) [PMID: 16606617].

GO terms

Biological Process

GO:0006355 regulation of transcription, DNA-templated
GO:0006351 transcription, DNA-templated

Molecular Function

No terms assigned in this category.

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.