H2AQ105 methylation, molecular mechanism of a novel histone modification

• Applicant: Professor Dr. Peter Tessarz
• Subject Area: General Genetics and Functional Genome Biology ; Biochemistry
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 326677350

We recently described glutamine methylation of histone H2A (here referred to as Qme) as a novel histone modification (Tessarz et al., Nature 2014). It is exclusively localised within the nucleolus over the rDNA transcriptional unit. We reported several lines of evidence that strongly suggested that this modification is the first modification described to date dedicated to a single polymerase, RNA Polymerase I. This finding is supported by a recently published report that could recapitulate major findings of our paper in plants (Loza-Muller et al., Front. Plant. Sci. 2015). We elucidated one particular biological function of this modification, which is the regulation of nucleosome deposition by the histone chaperone FACT in the wake of the travelling polymerase.Now, using quantitative mass spectrometry, we could identify the small subunit processome as being specifically recruited to Qme. This protein complex is required for the initial steps of pre-rRNA processing. These data are supported by RNA-Seq comparing WT and an H2AQ105A expressing mutant, in which specific deregulation of genes involved in ribosome biogenesis is highlighted. Following up on the MS data and by using recombinant protein, we could demonstrate that Nhp2 is a direct binder for methylated glutamine. Nhp2 is a core component of an H/ACA snoRNA-guided pseudouridinylation complex that converts uridines to pseudouridines within the rRNA. This is crucial for ribosome fidelity. Furthermore, we present preliminary evidence that the levels of Qme are changing with the cell cycle and that they are dependent on a crosstalk with another histone modification, H3K56 acetylation.In this project, we will expand on this preliminary dataset and seek answers to the following outstanding questions: i) how does Nhp2 specifically bind only methylated glutamine and does it serve as an adaptor to recruit the whole pseudouridinylation complex to rDNA, ii) how do H3K56ac and H2AQ105me communicate and which pathways are integrated, and iii) how does methylation of H2AQ105 modulate the histone chaperone activity of FACT on a molecular basis?

• DFG Programme: Research Grants