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Phosphorylation of Chromatin-associated Proteins in Lemna and Hordeum¹

^a Michigan State University-Atomic Energy Commission Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824

Sterile embryos of barley (Hordeum vulgare) and cultures of Lemna perpusilla have been labeled with ³²Pi and the chromatin proteins prepared and separated by acid-urea and sodium dodecyl sulfate gel electrophoresis. Under these conditions chromatin proteins became labeled and the gel radioactivity profiles which were complex indicated a probable minimum of 15 to 20 proteins phosphorylated with molecular weights ranging from 10⁴ to 10⁵. The majority of the radioactivity, 80 to 90% of the total, is found in the acidic protein fraction and this can be recovered as serine phosphate after partial acid hydrolysis.

Nuclei have been isolated from Lemna and barley and found to possess endogenous kinase activity. In vitro labeling of these nuclei with ³²P-adenosine triphosphate indicated that similar proteins appear to become labeled as in vivo labeling with ³²Pi but the proportions of label in each protein were different.

³ Present address: Department of Botany, University of Edinburgh, Edinburgh, Scotland.

¹ This research was supported by the United States Atomic Energy Commission under Contract AT-(11-1)-1338.