Quick and facile preparation of histone proteins from the green microalga Chlamydomonas reinhardtii and other photosynthetic organisms.

The development of universal, broadly applicable methods for histone extraction from animal cells and tissues has unlocked the ability to compare these epigenetic-influencing proteins across tissue types, healthy and diseased states, and cancerous versus normal cells. However, for plants and green algae, a quick and easily implemented histone extraction method has yet to be developed. Here, we report an optimized method that provides a unified approach to extract histones for the green microalgal species Chlamydomonas reinhardtii and Scenedesmus dimorphus as well as for maize (corn) leaf tissue. Histone extraction methods include treatment with high salt concentrations and acidification. Preparations of nuclei can be made in ∼3.5 h and histones extracted in ∼3.5 h either immediately or nuclei may be frozen and histone proteins can be later extracted without a change in histone PTM patterns. To examine the efficiency of the new methods provided, we performed both qualitative and quantitative analysis of salt and acid-extracted whole histone proteins (SAEWH) via SDS-PAGE gel electrophoresis and intact protein mass spectrometry. SDS-PAGE analysis indicated that histone yields decrease when using walled Chlamydomonas strains relative to cell-wall-less mutants. Using top-down mass spectrometry (TDMS) for intact protein analysis, we confirmed the presence of H4K79me1 in multiple algal species; however, this unique modification was not identified in corn leaf tissue and has not been reported elsewhere. TDMS measurements of SAEWH extracts also revealed that oxidation which occurs during the histone extraction process does not increase with exposure of harvested algal cells, their nuclei and the extracted histone samples to light.