The Structure of Eukaryote Chromatin

Abstract

In this paper certain aspects of the structure of chromatin are considered, with emphasis on the relationships of histone and residual protein to DNA. Recent findings relative to the complexing of histone with DNA are reviewed and material from this laboratory concerning the ratio of total histone to DNA and related topics are discussed. The questions of DNA strandedness and DNA repeating sequences are considered briefly. The relationship of residual protein of the cell nucleus to the structure of the chromosome is taken up and the bearing of the results of studies of nuclear gels on this problem are discussed. Recent results from this laboratory on the use of shear and a new autolytic procedure for detaching DNA from residual protein are outlined. The failure of residual protein to cause a marked elevation in the tm of nuclear DNA is discussed and material on the density gradient centrifugation of the DNA-residual protein complex is presented. Recent work on the fractionation of residual protein obtained from chromatin and isolated nuclei is critically reviewed. Finally a new hypothesis concerning a protein core structure in eukaryote chromosomes is presented briefly in the form of a model which may help to rationalize previously unexplained observations.

High total histone/deoxyribonucleic acid ratios for rat liver nuclei

“…Nuclei isolated in sucrose at pH 3.8 and 5.8 and DNA-residual protein complex from these nuclei form good gels, which are stable under the conditions previously stated by us to be criteria for demonstrating that the gels have not been partially degraded (Dounce et al, 1957;Mackay et al, 1968). Further details of the formation and properties of nuclear gels are given by Volkman & Dounce (1972) and Dounce et al (1972). The nuclei isolated at pH 3.8 in sucrose form particularly stable gels.…”

“…It cannot yet be stated why the effects of low pH or CaCl2 or both on rat liver nuclei differ, depending on whether they are imposed on already isolated nuclei or nuclei suspended in the original liver homogenate. These questions have been discussed previously (Chanda & Dounce, 1971c;Dounce et al, 1972).…”

“…Some of the possible implications of the presence of an extra amount of histone in liver nuclei isolated at pH3.8 or 5.8 or the loss of approximately half the histone complement when liver nuclei are isolated at pH 3.1 or in the presence of CaCl2 without pH adjustment have been discussed previously (Dounce & Ickowicz, 1969;Chanda & Dounce, 1971c;Dounce et al, 1972). We cannot say at the present time how the extra complement of histone is bound in liver nuclei when it occurs, but the observation of Phillips (1968) and Paul & More (1972) that calf thymus chromatin can bind an extra complement of histone when suspended in a solution of free histone may have bearing on this point.…”

Molecular Mechanism of Action of the Male Sex Hormones

“…The above conclusion is arrived at after considering the extraordinary complexity of the eukaryotic transcriptional process, the expression of which is determined by the interaction of various molecules. Among these is chromatin (Britten & Davidson, 1969;Crick, 1971 ; Dounce, Chanda, Ickowicz, Volkman, Palermiti & Turk, 1972;Paul, 1972;Biswas, 1974), a diversity of proteins with different functional and structural activities, such as RNA polymerases (Chambón, Gissinger, Kedinger, Mandel, Meilhac & Nuret, 1972), acidic chromosomal proteins (Chaudhuri, Stein & Baserga, 1972) and histones (De Lange & Smith, 1971) and finally other molecules which regulate the genetic programme and its expression (Britten & Davidson, 1969). The stimulation of RNA synthesis observed after hormone administration could be con¬ sidered as the result of actions at any of the following levels connected with RNA synthesis : chromatin template activity or capacity (Paul, 1972), RNA polymerase activity (Chambón et al 1972), RNA transport from nucleus to cytoplasm (Tata, 1966;Samarina, Lukanidin & Georgiev, 1973), pool size of RNA precursors (Tata, 1966) and turnover rate of different RNA species (Burdon, 1971 ;Kenney, Lee & Stiles, 1972).…”

The Mechanism of Giemsa-Banding of Mammalian Chromosomes, With Special Attention to the Role of Non-Histone Proteins

“…In this connection, it should be noted that non-histone proteins rich in SS-bond form a thermostable, residual complex with DNA (Dounce et al 1966(Dounce et al , 1972. A similar interpretation has been drawn by Utakoji 1972), whose banding technique involving a treatment with potassium permanganate was a cytochemical method extensively used for detection of SS and SH bonds (Dempsey et al 1950;Pearse 1951Pearse , 1953.…”