Chromatin protein modification: An epigenetic mechanism in the archaeon Sulfolobus solfatarticus

All living organisms face the challenge of packaging their DNA into the small space within the cell while still allowing access to the genetic information by molecular machinery for DNA replication, chromosome segregation, and gene expression. Organisms from each domain of life have evolved distinct mechanisms specifically designed for chromosomal organization and compaction. In all three biological domains classes of small, basic and abundant proteins bind DNA with little or no sequence specificity, and serve essential roles in the compaction, coiling, and regulation of gene expression. These proteins are also capable of undergoing post-translation modification at both N-terminal and internal ϵ-amino acid residues throughout their sequence and have been shown to be involved in the essential nuclear processes transcription, DNA replication and repair. Post-translational modification (PTM) of chromatin proteins is a well-documented phenomenon in Eukaryotes and Archaea. In eukaryotic systems PTM patterns of histone proteins has been shown to be reversible, heritable and involved in multiple cellular functions. A definitive role in prokaryotic organisms has yet to be discovered. The similarities in chromatin function between eukaryotes and archaeal lineages suggest that a similar level of regulation may exist in archaea, however, archaeal chromatin PTMs have not been linked to a cellular function. Preliminary studies have revealed the occurrence of multiple small, basic chromatin proteins in the archaeon Sulfolobus solfataricus (Sso) as well as the likelihood of PTMs playing a role in catabolite repression and extreme acid-resistance through regulation of gene expression. To understand the evolutionary implications of post-translational modification of chromatin proteins and its possible functional significance in members of the phylum Crenarchaeota, this project examined the PTM state of native chromatin proteins in vivo and their genome occupancy patterns. The analysis of chromatin and modifying proteins in wild-type and super acid-resistant cell lines of Sso have helped locate a mechanistic coupling between modification state and phenotypic differences in acid evolved isolates. This information provides insight into the mechanism that regulates chromosome structure and gene expression in prokaryotes as well as the evolutionary significance of chromatin and epigenetic mechanisms