Nucleosomes are complexes of DNA and histone proteins that form the basis of eukaryotic chromatin. Eukaryotic histones are descended from Archaean homologs; however, how this occurred remains unclear. Our previous genetic analysis on the budding yeast nucleosome identified 26 histone residues conserved between S. cerevisiae and T. brucei; 15 that are lethal when mutated and 11 that are synthetically lethal with deletion of the FEN1 nuclease. These residues are partially conserved in nucleosomes of a variety of giant viruses, allowing us to follow the route by which they were established in the LECA (Last Eukaryote Common Ancestor). We analyzed yeast nucleosome genetic data to generate a model for the emergence of the eukaryotic nucleosome. In our model, histone H2B-H2A and H4-H3 doublets found in giant virus nucleosomes facilitated the formation of the acidic patch surface and nucleosome entry sites of the eukaryotic nucleosome, respectively. Splitting of the H2B-H2A doublet resulted in the H2A variant, H2A.Z., and subsequent splitting of the H4-H3 doublet led to a eukaryotic specific domain required for chromatin binding of H2A.Z. We propose that the LECA emerged when the newly-split H3 N-terminal horizontally acquired a common N-tail found in extinct pre-LECA lineages and some extant giant viruses. This hypothesis predicts that the emergence of the H3 variant CENP-A and establishment of CENP-A-dependent chromosome segregation occurred after the emergence of the LECA, implying that the root of all eukaryotes is assigned within Euglenida.

Yu Nakabayashi

Masayuki Seki

Genes & Genetic Systems

基因与遗传系统，前身为日本遗传学杂志，由日本遗传学会出版双月刊。

Genes and Genetic Systems is a bimonthly journal published by the Japanese Society of Genetics, formerly known as the Japanese Journal of Genetics, focusing on research in genes and genetic systems.

《Genes and Genetic Systems》是由日本遗传学会出版的双月刊，前身为日本遗传学杂志，专注于基因与遗传系统的研究。

Category	Quartile
生物学	4
生物学, 生化与分子生物学	4
生物学, 遗传学	4

A hypothesis of nucleosome evolution considering mutational analysis

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Journal Info

Category	Quartile
GENETICS & HEREDITY	4