ProHistoneDB: A database of prokaryotic and viral histones

Histones are one of the fundamental chromatin proteins of life. In eukaryotes and megaviruses, they form nucleosome structures that wrap DNA. However, in prokaryotes, histones are much more diverse in how they organize DNA. In bacteria, histones bend and wrap DNA while in archaea they wrap and bridge DNA. These differences in DNA organizing properties are primarily due to distinct modes of histone multimerization. Here we present ProHistoneDB, an online database describing and categorizing prokaryotic and viral histones. For each histone, monomer, dimer, tetramer, and hexamer predictions are viewable and downloadable. ProHistoneDB contains 7334 histones, categorized into 24 groups based on the multimer predictions. For each category, interactive phylogenetic trees and HMM profile logos are available to identify conserved residues and explore the relative evolutionary relationships of histones. ProHistoneDB can be accessed at https://prohistonedb.org/.