# Control of Gene Expression by Proteins That Bind Many Alternative Nucleic Acid Structures Through the Same Domain

## TL;DR

This paper explores how proteins that bind to DNA can also interact with alternative DNA structures, suggesting a new mechanism for gene regulation.

## Contribution

The study reveals that transcription factors can bind to alternative nucleic acid structures, expanding our understanding of gene regulation.

## Key findings

- Computational modeling shows that B-DNA-binding transcription factors also dock to alternative structures like Z-DNA and GQ.
- Methylarginine modifications promote the binding of HLH and bZIP homodimers to Z-DNA.
- Binding to alternative structures may help transcription factors find their target sites in active genes more efficiently.

## Abstract

The role of alternative nucleic acid structures (ANS) in biology is an area of increasing interest. These non-canonical structures include the Z-DNA and Z-RNA duplexes (ZNA), the three-stranded triplex, the four-stranded G-quadruplex (GQ), and i-motifs. Previously, the biological relevance of ANS was dismissed. Their formation in vitro often required non-physiological conditions, and there was no genetic evidence for their function. Further, structural studies confirmed that sequence-specific transcription factors (TFs) bound B-DNA. In contrast, ANS are formed dynamically by a subset of repeat sequences, called flipons. The flip requires energy, but not strand cleavage. Flipons are enriched in promoters where they modulate transcription. Here, computational modeling based on AlphaFold V3 (AF3), under optimized conditions, reveals that known B-DNA-binding TFs also dock to ANS, such as ZNA and GQ. The binding of HLH and bZIP homodimers to Z-DNA is promoted by methylarginine modifications. Heterodimers only bind preformed Z-DNA. The interactions of TFs with ANS likely enhance genome scanning to identify cognate B-DNA-binding sites in active genes. Docking of TF homodimers to Z-DNA potentially facilitates the assembly of heterodimers that dissociate and are stabilized by binding to a cognate B-DNA motif. The process enables rapid discovery of the optimal heterodimer combinations required to regulate a nearby promoter.