The C-Domain of the NAC Transcription Factor ANAC019 Is Necessary for pH-Tuned DNA Binding through a Histidine Switch in the N-Domain

The affinity of transcription factors (TFs) for their target DNA is a critical determinant of gene expression. Whether the DNA-binding domain (DBD) of TFs alone can regulate binding affinity to DNA is an important question for identifying the design principle of TFs. We studied ANAC019, a member of the NAC TF family of proteins in Arabidopsis, and found a well-conserved histidine switch located in its DBD, which regulates both homodimerization and transcriptional control of the TF through H135 protonation. We found that the removal of a C-terminal intrinsically disordered region (IDR) in the TF abolished the pH-dependent binding of the N-terminal DBD to DNA. We propose a mechanism in which long-range electrostatic interactions between DNA and the negatively charged C-terminal IDR turns on the pH dependency of the DNA-binding affinity of the N-terminal DBD.