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HB1, ASXL, restriction endonuclease HTH domain 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. 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. 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. 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. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",