# The Lrs14‐Like AbfR1 Homolog From Metallosphaera sedula Is a Nucleoid‐Organizing Protein

## TL;DR

This study shows that the AbfR1 protein in Metallosphaera sedula helps organize DNA in a way similar to bacterial proteins.

## Contribution

The study reveals a structural role for AbfR1 in nucleoid organization, expanding its known functions beyond gene regulation.

## Key findings

- AbfR1Ms binds DNA non-sequence specifically and associates with AT-rich regions genome-wide.
- AbfR1Ms induces DNA condensation and aggregation, suggesting a role in chromatin architecture.
- The findings imply functional similarity between AbfR1Ms and bacterial nucleoid-associated proteins.

## Abstract

Nucleoid organization in Crenarchaeota is mediated by a plethora of diverse families of small DNA‐binding proteins. However, the role of the Lrs14 family, a prevalent family of small DNA‐binding proteins within the Crenarchaeal order of the Sulfolobales, remained rather ambiguous. Previous studies have focused on gene regulatory functions of the Lrs14 family and have shown that the Lrs14‐type protein AbfR1 is involved in the regulation of biofilm formation and motility in the model species Sulfolobus acidocaldarius. In this study, we set out to investigate the DNA‐binding characteristics of the AbfR1 homolog in Metallosphaera sedula, a related mixotrophic species within Crenarchaeota. AbfR1
Ms
and AbfR1
Sa
share 50% amino acid sequence identity and are structurally very similar. We observed that heterologously purified AbfR1
Ms
forms dimers in solution and binds DNA in vitro in a non‐sequence‐specific manner with diverse DNA probes. Chromatin immunoprecipitation combined with high‐throughput sequencing revealed an association of AbfR1
Ms
with numerous sites across the genome of M. sedula. This genome‐wide association was found to correlate with adenine‐thymine‐rich regions and possibly with the global chromatin structure, rather than with specific DNA sequences. Notably, the most highly enriched AbfR1
Ms
binding sites were characterized by extended DNA regions spanning several thousand base pairs. Atomic force microscopy further demonstrated that AbfR1
Ms
promotes DNA condensation and aggregation, suggesting a role in chromatin architecture. These findings suggest that AbfR1
Ms
, and possibly other related Lrs14 members, play a critical role in nucleoid organization, with properties resembling those of bacterial nucleoid‐associated proteins.

Nucleoid organization in Crenarchaeota involves diverse small DNA‐binding proteins. The Lrs14‐type protein AbfR1 from Metallosphaera sedula binds nonsequence specifically across the genome and induces DNA condensation. These findings suggest a structural role for AbfR1Ms in chromatin architecture, functionally resembling bacterial nucleoid‐associated proteins.