Fig. 3. Potential mechanisms for the substrate switching by Hda1C. Hda1C specifically deacetylates histone H4 and H3 at hyperactive and inactive genes, respectively. The specificity of this complex may be regulated by posttranslational modifications of Hda1 and Hda3 including sumoylation and phosphorylation. In addition, Hda1C is highly enriched at hyperactive genes but not at inactive genes. This difference in local concentrations of this complex may also affect the substrate switching of Hda1C. Finally, both Hda2 and Hda3 have the ability to bind to RNAs. At hyperactive genes, Hda1C may interact with mRNAs, resulting in H4-specific deacetylation. As most inactive genes are associated with lncRNA transcription from either an upstream or an antisense promoter, Hda1C may directly bind to lncRNAs transcribed from inactive genes to enhance deacetylation of histone H3.
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