PONTECORVO1 in his Leeuwenhoek lecture to the Royal Society said that “histones are characteristic intranuclear proteins in search of employment”. Other workers have suggested that histones could be concerned with the regulation of RNA synthesis2,3. The findings of Gurley et al.4 were more specific. They found that in a cell-free system. DNA polymerase was inhibited by a lysine-rich histone fraction. Our own work points in the same direction. During a study of the cellular control of metabolism we isolated basic proteins of Escherichia coli and found that some of these preparations inhibited the organism from which the protein was isolated.