An X-ray diffraction study of histone and protamine in isolation and in combination with DNA

Interaction of DNA with lysine-rich polypeptides and proteins. The influence of polypeptide composition and secondary structure

Using X-ray diffraction we have studied fibres obtained from complexes of DNA with lysine-rich polypeptides and with proteins that have different conformations, to ascertain whether the conformations of the polypeptides and the DNA are maintained upon interaction. Substances investigated include N-acetyl-Lys-Ala-Tyr-Ala-Lys-ethylamide, random poly(Leu50, Lys50), sequential poly(Leu-Lys), poly(Val-Lys), poly(Ala-Lys), poly(Lys-Ala-Ala-Lys), poly(Lys-Ala-Ala), poly(Lys-Leu-Ala), poly(Lys-Ala-Gly), protein phi 0 from sea cucumber spermatozoa, histone H1 and two fragments of this protein obtained by chemical cleavage. In general, the B form of DNA with ten base-pairs per helical turn is maintained upon interaction at high levels of humidity. The A form is never observed; it appears to be forbidden in a protein environment. No evidence for transition into any novel DNA conformation has been observed, although the B form is altered in some cases, in particular upon dehydration. Such alteration occurs always in the sense of tightening the double helix, so that the number of base-pairs per helical turn diminishes. The polypeptides may interact with DNA in both the alpha and beta conformations. We have found different types of complexes in which either a monolayer or a double layer of beta-pleated sheets is intercalated between layers of DNA molecules. Alternatively, the polypeptide chain may be wrapped around the DNA, following one of the grooves. The polypeptide conformation may be either maintained or changed upon interaction. The charge density of the polypeptide is an important parameter of the interaction. When it matches the charge density of the DNA, the polypeptide conformation is maintained in most cases; otherwise it is modified. The globular part of histone H1 gives a unique X-ray pattern upon interaction, indicative of a loss of order of DNA in the complex. On the other hand, the C-terminal part of histone H1 gives a very well-ordered complex, similar to a nucleoprotamine, in spite of its lower charge density.

Structural heterogeneity of reconstituted complexes of DNA with typical and intermediate protamines

The binding of the intermediate proteins phi 1 and phi 3 from the mussel Mytilus edulis to DNA was studied in comparison with the typical protamine from the squid Loligo vulgaris using precipitation curves, thermal denaturation and X-ray diffraction techniques. The properties of protein phi 1 appear to be very close to those of typical protamines while the properties of protein phi 3 are notably different. The method of reconstitution influences the structural properties of the complexes. This effect is most pronounced in the case of protein phi 3. The structural heterogeneity of the protein component in the complexes is discussed in the light of these observations.

Light microscopic demonstration of myoid material in nuclei

During the development of configurational staining methods for proteins of the myosin-fibrin group, nuclei showed staining properties similar to those of myofibrils. This dye binding could be attributed to nuclear alpha-helical proteins. More recent chemical and electron microscopic studies demonstrated actomyosins in nuclei of various species. Possible roles of nuclear actomyosin in chromosome movements and condensation and in cell proliferation have been suggested. It seems therefore permissible to assume that the tannic acid-phosphomolybdic acid (TP)-Levanol Fast Cyanine 5RN method and similar technics visualize myosin in nuclei. Comparative studies of actomyosins from various sites indicated significant chemical an histochemical differences. It is therefore suggested that, in analogy to the different classes of collagens, there may be several subgroups of myosin which differ in their physico-chemical properties and sensitivity to fixation procedures and pathological conditions.

The subunit structure of the eukaryotic chromosome

New strucutral data have been obtained from neutron scattering studies of chromatin. The concentration-dependent meridional peak at 10-11 nm comes from the interparticle spacing of a subunit structure. Peaks at 5.5 and 3.7 nm have a different contrast behaviour to those at 11.0 and 3.7 nm showing that histones and DNA have a different spatial arrangement in the subunit. A globular model in which apolar segments of histones from the core surrounded by DNA complexed with the basic segments of histones agrees with the data.

CYCLIC STRUCTURE OF ADENOVIRUS DNA

The deoxyribonucleic acids of adenovirus types 2, 7, and 12 were extracted and examined in the electron microscope. Cyclic forms of the molecules were found to exist in each viral type. The lengths of cyclic strands extracted from the most dense fraction of purified particles of adenovirus type 2 were highly variable, averaging about 2.5 microns. This corresponds to a molecular weight of about 5 million.