Optical Activity of Nucleoproteins and Histones

Abstract

Nucleoproteins are complex macromolecular substances composed of deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) and histones. While DNA is known to be the carrier of the genetic code, the role of histones is still imperfectly understood. Two main functions of histones have been considered: (1) regulation of gene activity, either by suppressing DNA replication or by controlling DNA-dependent RNA synthesis, and (2) regulation of the structural integrity of the nucleoprotein complex as a building block for chromosomes. Histones are composed chiefly of alanine, arginine, and lysine; and, because of the excess of basic groups at their side chains (R-groups), they react with nucleic acids. According to Zubay and Doty (1959), the histones in the DNA—protein complex are largely in helical form with their basic side chains electrostatically linked to the phosphate groups of DNA, and they fill the major groove in double-stranded DNA. On the basis of X-ray diffraction studies, Wilkins, Zubay, and Wilson (1959) suggested that intra- and inter-DNA histone bridges control the multistranded organization in the chromosomes. Extensive recent reviews on nucleoproteins and histones are available (Bonnerand Ts’o, editors, 1964; Busch, 1965; Phillips, 1971; Hnilica, 1967, 1972).