Mapping of lysine methylation and acetylation in core histones of Neurospora crassa.

Core histones are susceptible to a variety of post-translational modifications (PTMs), among which methylation and acetylation play critical roles in various chromatin-dependent processes. The nature and biological functions of these PTMs have been extensively studied in plants, animals, and yeasts. In contrast, the histone modifications in Neurospora crassa, a convenient model organism for multicellular eukaryotes, remained largely undefined. In this study, we used several mass spectrometric techniques, coupled with HPLC separation and multiple-protease digestion, to identify the methylation and acetylation sites in core histones isolated from Neurospora. Electron transfer dissociation (ETD) was employed to fragment the heavily modified long N-terminal peptides. In addition, accurate mass measurement of fragment ions allowed for unambiguous differentiation of acetylation from trimethylation. Many modification sites conserved in other organisms were identified in Neurospora. In addition, some unique modification sites in histone H2B, including N-terminal alpha methylation, methylation at K3, and acetylation at K19, K28, and K29, were observed. Our analysis provides a potentially comprehensive picture of methylation and acetylation of core histones in Neurospora, which should serve as a foundation for future studies of the function of histone PTMs in this model organism.