Overview
Abstract
Chromatin is regarded as a DNA-compacting eukaryotic hallmark, yet studies have identified histone homologs in archaea, organisms encoded by bacterial-sized genomes and lacking a nuclear envelope. We report the first archaeal nucleosome occupancy map, as observed in the halophile Haloferax volcanii. Nucleosome occupancy was compared with gene expression by compiling a transcriptome of Hfx. volcanii. We found that archaeal transcripts possess hallmarks of eukaryotic chromatin structure: nucleosome-free regions at transcriptional start sites and conserved -1 and +1 promoter nucleosomes. The similarity of basic chromatin structure in archaea is striking due to the higher gene density, lack of 5' UTRs and lack of C-terminal tails in histones that are known to store the histone code in eukaryotes. Our observations demonstrate that histones and chromatin architecture evolved before the divergence of Archaea and Eukarya, suggesting that the fundamental role of chromatin in the regulation of gene expression is ancient.