On conformations of the superhelix structure

The slight deformation of a helical macromolecule leading to the superhelical structure is considered. General equations which connect “internal” stereochemical parameters of the backbone of a helical macrcmolecule with “external” parameters of the superhelix are obtained; they are analogous to those of Shimanouchi and Mizushima. The case when the radius of the major helix is much greater than the radius of the minor helix is treated. Assuming that all conformational changes are due to small distortions of the rotation angles (bond angles and bond lengths are kept constant) the general equations reduce to a set of nonhomogeneous linear algebraic equations. Its solution (in the case of the DNA double-helix in B-form) shows that the DNA backbone can form a coiled-coil with parameters close to those estimated from experimental data on DNP in chromatine from nuclei of cells.     

On the fine structure of polyribosomes

Cell and Tissue Research - The ultrastructural morphology of ribosomes was studied in tissue sections of rat uterus using different fixatives (acrolein, formaldehyde, acetic acid, methanol-acetic...     

On the structure of proteoglycan core

Core protein from bovine nasal proteoglycan has been obtained by cyanogen bromide cleavage and by removal of most of the glycosaminoglycan side chains by hydrogen fluoride treatment. Amino acid analysis of the cyanogen bromide fragment shows it to consist mainly of proline, serine, glycine and glutamic acid (glutamine). End-group analyses of the fragment and HF stripped core reveal and N-terminal residue to be valine in each case. The stripped core has been subjected to sequencing and some sequential information is presented. Based upon the amino acid analysis, sequence information and other properties, conformation analysis indicates that the most likely conformation is that of a flexible extended chain containing β-turns. The existence of a common N-terminal residue indicates that it is the C-terminal region which lies in the region of the hyaluronic acid backbone in intact proteoglycan. Furthermore, enzymatic cleavage of core protein which occurs in proteoglycan turnover, aging and degenerative diseases, probably does not occur by a stepwise cleavage from the N terminus of proteoglycan but by a more drastic degradation process.     

On the structure of coated vesicles

Electron micrographs of tilted specimens of coated vesicles show that their coats are based on polyhedral lattices constructed from 12 pentagons plus a variable number of hexagons. We have identified three such structures among the smaller particles, two containing 108 molecules of clathrin and a third containing 84. The coats of larger particles are believed to be constructed on similar principles. This polymorphism enables a variety of vesicles to be accommodated in an economical manner.     

On the molecular structure of chromosomes

Summary It is suggested that the construction of molecular models of the chromosome may prove to be a fruitful way of attacking the fundamental problems of cytology and genetics. Certain micelles consisting of molecules of protamine-nucleate are suggested for consideration. They are designed to interpret in molecular terms the postulates of genetics and the nature of the gene, and are constructed with special reference to the findings of the cytologists as to the capacity of the chromosomes to swell, to contract, to grow and to divide.Based upon a lecture given in the physics department of the University of Manchester on May 13, 1935. The Author is indebted to W. T.Astbuby, L. E.Bayliss, J. D.Bernal, D.Crowfoot, C.D.Darlington, P.& G.Eggleton, J.M.Gulland, L.J.Harris, D.Jordan Lloyd, M. F.Howson, W. O.Kermack, E. H.Neville, M.Polanyi and J. Z.Young for advice and criticism.     

On the structure of liver ribosomes

The morphology of liver ribosomes and their subparticles, large and small, has been investigated. Analysis of the images has been carried out by successive selection of models and by X-raying them under conditions simulating negative staining. The relation between the main views has been checked by tilting the specimens in an electron microscope through ± 30 °.The small subparticle consists of an elongated body, to one of the ends of which a short “head” is attached. A model has been proposed, whose projections on rotation with respect to the longitudinal axis would satisfy all observable types of images. According to the proposed model, the “head” is tilted with respect to the elongated portion. The length of the subparticle is 230 Å. The dimensions of the elongated portion in the transverse direction are 110 Å × 75 to 80 Å.The large subparticles in lateral view resemble short “rods” 220 to 240 Å long and about 70 to 95 Å wide. At a distance of about 60 Å from the left end of the particles a projection (60 Å in length) is seen, on the inner side of which a depression, or “channel”, filled with the contrasting substance is always observed. Next to this depression a second projection is located, whose height is about 30 Å. The channel is either a cavity in the body of the large subparticle or a part of the RNA without protein. The length of the channel is about 80 Å, the width is about 50 to 60 Å. The left end of the particles is characterized by two sharpened portions; as a result, a cavity that shows an obtuse angle profile makes its appearance. The opposite end of the particles is cut off at an angle of 45 °. In another view, the subparticles appear to be almost rectangular in shape; they are characterized by dimensions of 150 Å × 220 to 240 Å. It is likely that the large projection is displaced sideways with respect to the longitudinal axis of the particles. The asymmetry associated with this displacement gives rise to preferred arrangements of the subparticles on the supporting film. An analysis has been made of the most typical images of monomeric ribosomes, on the basis of which a suggestion is made about mutual orientation of subparticles in a monomer.     

On the inflorescence structure ofAsclepiadaceae

Inflorescence structure in the familyAsclepiadaceae, particularly in the subfamilyAsclepiadoideae, is elucidated using the methodology and terminology of the school ofW. Troll. Asclepiadaceae inflorescences are principally thyrsoid systems, with variability resulting from different degrees of reduction of dichasial paracladia to bostryces, sciadioids, and, finally, to single flowers.