Phosphorylation and chromatin mechanics: the central importance of substrate conformation in determining the patterns...

HL-60 nuclear autophosphorylation was studied in vitro under circumstances in which the conformation of chromatin was manipulated with both polyamines and DNAse-I. A general re-arrangement of the phosphorylation patterns occurred as polyamines were removed and nuclei were observed to expand. DNAse-I treatment reduced these phosphorylation patterns to a much simpler configuration indicating that the responding substrates were DNA-associated. It was concluded that substrate conformation was the main determining factor in the control of nuclear protein phosphorylation. These results suggest a method of general utility for the identification of truly nuclear proteins by the characteristics of their phosphate acceptor activity.