Atomic Force Microscopy in Imaging of Viruses and Virus-Infected Cells

Summary: Atomic force microscopy (AFM) can visualize almost everything pertinent to structural virology and at resolutions that approach those for electron microscopy (EM). Membranes have been identified, RNA and DNA have been visualized, and large protein assemblies have been resolved into component substructures. Capsids of icosahedral viruses and the icosahedral capsids of enveloped viruses have been seen at high resolution, in some cases sufficiently high to deduce the arrangement of proteins in the capsomeres as well as the triangulation number (T). Viruses have been recorded budding from infected cells and suffering the consequences of a variety of stresses. Mutant viruses have been examined and phenotypes described. Unusual structural features have appeared, and the unexpectedly great amount of structural nonconformity within populations of particles has been documented. Samples may be imaged in air or in fluids (including culture medium or buffer), in situ on cell surfaces, or after histological procedures. AFM is nonintrusive and nondestructive, and it can be applied to soft biological samples, particularly when the tapping mode is employed. In principle, only a single cell or virion need be imaged to learn of its structure, though normally images of as many as is practical are collected. While lateral resolution, limited by the width of the cantilever tip, is a few nanometers, height resolution is exceptional, at approximately 0.5 nm. AFM produces three-dimensional, topological images that accurately depict the surface features of the virus or cell under study. The images resemble common light photographic images and require little interpretation. The structures of viruses observed by AFM are consistent with models derived by X-ray crystallography and cryo-EM.     

Mechanism of inactivation and mutagenesis induced by ethyleneimine in Drosophila germ cells. V. Relation of complete and mosaic mutations during the supplementary action of high temperature]

Supplementary effect of high temperature (37 degrees C) an hour after the treatment of mature sperms of Drosophila with ethylene imine resulted in an increased level of the inactivation (the frequency of dominant lethal mutation). The frequency of complete mutations (recessive sex-linked lethal mutations) increased by the supplementary effect of high temperature at low doses of E1, and it did not change under a comparatively high dose of the mutagen. The frequency of mosaic mutations decreased under the effect of high temperature at both doses of E1. No effect of high temperature was observed in 4 and 24 h after the E1 treatment. The results obtained are discussed in connection with the proportion of inactivation and mutagenesis under the effect of chemical mutagens on Drosophila germ cells.     

Mathematical model of histamine bronchospasm]

A mathematical model of changes in histamine concentration in the wall of human bronchiole was constructed. The parameters of the model adequately characterize the state of patients with bronchial asthma.     

Alterations in the creatine kinase system in the myocardium of cardiomyopathic hamsters

Immunochemical and biochemical methods were used to assess quantitatively the changes in the heart creatine kinase system in the myopathic Syrian hamsters, line CHF I46. Cardiomyopathy in I75-200 day old animals was characterized by decreased content of mitochondria and lower total creatine kinase activity. In isolated mitochondria only the creatine kinase activity was decreased while cytochromes aa3 content and respiration rate were unchanged. The share of mitochondrial creatine kinase in the total tissue enzyme activity was decreased from 33% to I8% and that of BB form was elevated from 5% in control to 20%, at unchanged relative level of MM. Immunoassay showed decreased amount of the mitochondrial creatine kinase in the tissue and its decreased ratio to cytochromes aa3. The results show altered expression of creatine kinase isoenzymes in cardiomyopathy.     

Action of microwaves with different modulation frequencies and exposure times on GABA receptor concentration in the cerebral cortex of rats]

The effect of 800 mHz microwaves of 0, 3, 5, 7, 16, and 30 Hz modulation on GABA receptor concentration in rat brain cortex has been investigated. Irradiation of the whole body at a modulation frequency of 16 Hz readily decreases the GABA receptor concentration. Irradiation at other modulation frequencies is ineffective. Irradiation of the whole body modulated at 16 Hz with various exposure times (5, 15 and 60 min) has revealed the highest effect at 5 min, while at a longer exposure the effect decreases.     

Electrophysiological analysis of corticofugal influences on preoptic neurons

Evoked potential (EPs) and responses of the medial (MPO) and lateral (LPO) preoptic region (RPO) and adjacent structures of the hypothalamus to stimulation of the prefrontal (area 8) and cingulate (area 24) cortex, piriform lobe (periamygdaloid cortex), and hippocampus (area CA3) were investigated in acute experiments on cats under ketamine anesthesia. The most pronounced EPs were observed in the RPO after stimulating the piriform and cingulate cortex. A close relation was found between neuronal responses and EP components. The majority of neurons responding to stimulation of various cortical structures were localized in the LPO, where primarily excitatory responses dominate. The MPO contained somewhat fewer neurons responding to cortical stimulation, and the dominant response here was primarily inhibitory. The ratio of inhibitory and excitatory responses in the LPO was 0.6:1 and in the MPO 5.8:1. Primarily in-inhibitory responses dominated also in the LPO zone adjacent to the bed nucleus stria terminalis (BST) and primarily excitatory in the region surrounding the supraoptic nucleus (SO) (respective ratios 4.9:1 and 0.7:1). The RPO is a broad convergence zone, where 3/4 of the neurons responded to stimuli of two and more cortical regions.A. M. Gorky Medical Institute, Ukrainian Minstry of Health, Donetsk. Translated from Neirofiziologiya, Vol. 23, No. 6, pp. 709–719, November–December, 1991.     

The causes of hydration changes during DNA protonation

Changes of DNA hydration provoked by protonation in the way of Na+- and H+-ions exchange, and in the way of HCl addition to Na+-DNA, were analysed by IR-spectroscopy. Water is shown not to contribute essentially to the formation and stabilization of conformations arising when DNA is protonated. The differences between hydratation of DNA protonated by different ways are in the main accounted for by alteration of the quantities of Na+ and Cl- ions forming the aqueous-salt envelope of polynucleotide.     

Interaction of immobilized DNA with alkaline metal and ammonium ions

Ion exchangers with various capacities (0.1-0.2 mg-equiv/g of dry gel) are synthesized by means of immobilization of DNA in polyacrylamide gel. Exchanges of alkali metal cations and ammonium are studied on these exchangers and selectively coefficients are determined. The following selectivity series of immobilized DNA in reference to the above-mentioned cations is stated: Li+ greater than or equal to NH4+ greater than or equal to Cs+ greater than Rb+ greater than K+ greater than or equal to Na+. The peculiar properties of Li+ and NH4+ in this series are noted and a possible explanation of this fact is offered. A supposition regarding the reduced activity of water in the polyacrylamide gel containing DNA is made.