Acidic Solutions to Archaeal Chromatin

Abstract

Cells must organize their genomes to provide compact structure and coordinate genome regulation. Like eukaryotes, most known archaea also encode histones, albeit with shorter sequences (∼68 amino acids) that span only the three-helix motif without additional domains. Most studies of histone structure-function relationships in archaea have focused on hyperthermophiles, such as Thermococcus kodakorensis and Methanothermus fervidus, where histones have been observed to wrap DNA into long super-helical ramps, referred to as archaeasomes. On the other hand, how histones function in other archaea is not well understood, especially in species that encode histones that have acidic isoelectric points. Normally, such acidic proteins would not be thought to bind nucleic acids. However, these histones maintain a basic ridge that may facilitate DNA binding despite their global acidic character. Here, we utilize biophysical assays and computational models to explore how acidic archaeal histones bind DNA and structure chromatin. Understanding how these archaeal species utilize acidic histones is essential for mapping how pressures from extreme environments has driven histone evolution and diversification.