Bacterial histone HBb fromBdellovibrio bacteriovoruscompacts DNA by bending

Abstract

AbstractHistones are essential for genome compaction and transcription regulation in eukaryotes, where they assemble into octamers to form the nucleosome core. In contrast, archaeal histones assemble into dimers that form hypernucleosomes upon DNA binding. Although histone homologs have recently been identified in bacteria, their DNA-binding characteristics remain largely unexplored. Our study reveals that the bacterial histone HBb is indispensable for the survival ofBdellovibrio bacteriovorus, suggesting critical roles in DNA organization and gene regulation. We also elucidate the crystal structure of the HBb dimer at 1.06 Å resolution and employ various biophysico-chemical approaches to show its ability to bind and compact DNA in a sequence-independent manner. This binding induces DNA bending, similar to that observed with bacterial HU/IHF family proteins. Finally, using DNA affinity purification and sequencing, we reveal that HBb binds along the entire genomic DNA ofB. bacteriovoruswithout sequence specificity. These unique DNA-binding properties of bacterial histones, distinct from their archaeal and eukaryotic counterparts, highlight the diverse roles that histones can play in DNA organization across the domains of life.Author SummaryHistones, traditionally known for organizing and regulating DNA in eukaryotes and archaea, have recently been discovered in bacteria, opening up a new frontier in our understanding of genome organization across the domains of life. Our study investigates the largely unexplored DNA-binding properties of bacterial histones, focusing on HBb inBdellovibrio bacteriovorus. We reveal that HBb is essential for bacterial survival and exhibits DNA-binding akin to the bacterial nucleoid-associated HU/IHF family proteins. Contrary to eukaryotic and archaeal histones that wrap DNA, HBb bends DNA without sequence specificity. This work not only broadens our understanding of DNA organization across different life forms but also suggests that bacterial histones may have diverse roles in genome organization, distinct from their eukaryotic and archaeal counterparts.