PART I. INTERACTION OF DNA AND HISTONE IN NUCLEOHISTONE Chapter 1. SELECTIVE DISSOCIATION OF HISTONE FROM NUCLEOHISTONE With increasing concentration of NaCl solution, an increasing amount of histone is dissociated from dissolved nucleohistone. The dissociated histone fractions are identified by gel electrophoresis. The lysine rich histone fraction I is dissociated from nucleohistone in the range 0.3-0.5 F NaCl; slightly lysine rich histone II in the range 0.8-1.6 F NaCl; arginine rich histone III+IV in the range 0.9-1.6 F NaCl. The results suggest that both electrostatic and non-electrostatic interactions contribute to the strength of binding between DNA and histones. Chapter 2. OPTICAL ROTATORY DISPERSION STUDIES ON HISTONES The optical rotatory dispersion spectra of histones free and in reconstituted nucleohistone (in which histone is complexed to DNA) are recorded. By the criterion of optical rotatory dispersion at wavelengths below 220 mu, histone I is the least helical of the histones, histone II the most helical. The helicity of DNA-bound histones in reconstituted nucleohistone is greater than that of free histones, but the order, histone II most helical and histone I least, is still preserved. Chapter 3. OPTICAL ROTATORY DISPERSION STUDIES ON THE DNA OF NATIVE NUCLEOHISTONE AND OF PARTIALLY DEHISTONIZED NUCLEOHISTONES The conformation of DNA in native nucleohistone is altered by the DNA-histone interaction. The dissociation of histone I does not produce significant conformational change in DNA of nucleohistone but removal of histone II and of histone III+IV bring about changes which cause the conformation of DNA in nucleohistone to resume virtually that characteristic of free DNA. The possibility of DNA supercoiling in nucleohistone is discussed. PART II. DORMANCY ASSOCIATED WITH REPRESSION OF GENETIC ACTIVITY Chapter 1. THE DORMANCY OF POTATO BUDS Chromatin of the buds of dormant potato tubers is almost totally incapable of the support of DNA-dependent RNA synthesis in the presence of added exogenous RNA polymerase. The chromatin of non-dormant buds of potato tubers (in which dormancy has been broken by treatment with ethylene chlorohydrin) is highly effective in the support of DNA-dependent RNA synthesis by added exogenous RNA polymerase. It is therefore concluded that the genetic material of the buds of dormant potato tubers is largely in a repressed state, and that the breaking of dormancy is accompanied by derepression of the genetic material. Chapter 2. THE DORMANCY OF ONION BULBS The chromosomal material of non-growing and non-dividing onion buds possesses template activity in support of in vitro DNA-dependent RNA synthesis. If we define dormancy not only by the absence of visible growth and mitotic division, but also by the lack of ability to direct in vitro DNA-dependent RNA synthesis, potato buds are then dormant but onion buds are not. And the block to onion bud growth must lie somewhere else than in the repression of genetic material. Chapter 3. ISOLATION OF GLADIOLUS CHROMATIN Gladiolus corms contain very little isolatable chromatin material and the isolated chromatin is highly contaminated by the presence of starchy material.