A puzzle solved on the signals leading to the assembly or disassembly of histone H3.3-containing nucleosomes

A research team led by Prof. Yuda Fang, from Shanghai Institute of Plant Physiology and Ecology (SIPPE), Shanghai Institutes for Biological Sciences (SIBS), CAS, discovered that four amino acids guide the assembly or disassembly of Arabidopsis histone H3.3-containing nucleosomes. This work was just released ahead of print in PNAS (Proceedings of the National Academy of Sciences USA) on June 13th, 2011.

Histone H3 family contains canonical histone H3.1, histone variant H3.3 and centremere-specific histone CenH3, which are conserved from fly to human and plant. H3.3 is mainly associated with active chromatin by replacing H3.1 through chaperones such as HIRA, DAXX, ATRX or DEK and plays important roles in the germline, epigenetic memory and reprogramming. Arabidopsis histone H3.3 differs from H3.1 by four amino acid sites: amino acids 31 and 41 in the N-terminal tail and amino acids 87 and 90 in the core domain.

By comparing the dynamics of Arabidopsis histone H3.1, H3.3 and its mutated forms in transcriptionally active or inactive nucleolar chromatin, the team led by Prof. Fang proposed a model in which amino acids 87 and 90 in the core domain of H3.3 guide nucleosome assembly, while amino acids 31 and 41 in the N-terminal tail of Arabidopsis H3.3 guide nucleosome disassembly in nucleolar rDNA. The model is shown as follows:



(A model for the dynamics of Arabidopsis H3.3/HTR4 in nucleoli. The amino acid residues 87 and 90 in the core domain of H3.3 guide its deposition to active nucleolar chromatin, while the amino acid residues 31 and 41 in the N-terminal tail of H3.3 guide its depletion from the rDNA arrays when transcription is silenced.)

This research was supported by Grants from Chinese Academy of Sciences, National Natural Science Foundation of China, and the State Key Laboratory of Plant Molecular Genetics.