Mapping of deletions and substitutions in heteroduplex DNA molecules of bacteriophage lambda by electron microscopy

Electron microscopy of heteroduplex DNA molecules, composed of one strand of Escherichia coli phage lambda(+) DNA annealed to the complementary DNA strand of a lambda deletion or substitution mutant, permits visualization, as well as precise measurements and mapping, of the unpaired single-stranded regions of nonhomology in the otherwise double-stranded molecules. In the lambdab2 mutant, the central segment (13 percent) of the lambda(+) DNA molecule is shown to be deleted. In the hybrid phages lambda(i434) and lambda(i21) a segment of the right arm of the lambda(+) genome (5.5 or 7.6 to 9 percent) is replaced by the corresponding immunity regions of phage 434 (3.3 percent or phage 21 (4 percent) DNA. The b5 region in the lambdab5 mutant appears to be identical to the i(21) segment. From these data it is possible to estimate the size and posiion of those lambda genes which are replaced by the i(434) and i(21) segments. The method permits preparing complete physical maps of viral genomes with a precision heretofore unattainable.     

High-resolution electron microscopy of muscovite

Images of the (001) planes of muscovite were observed by electron microscopy after embedment of clay-size flakes in epoxy resin and sectioning by ultramicrotome. Dislocation or growth planes were indicated. Incomplete exchange of potassium for barium produced zones with 20-angstrom periodicity, suggesting regular interstratification.     

Scanning electron microscopy of evaporating ice

Direct observation of evaporating ice with a scanning electron microscope indicates that the surfaces of single-crystal and polycrystalline ice are markedly different. In specimens of single-crystal ice the crystal planes are revealed by evaporation, whereas polycrystalline ice develops a fibrous surface.     

Stereoscan electron microscopy of soil microorganisms

Details of the surface structure of microorganisms growing in soil and the complex topography of individual soil particles were observed with the Stereoscan electron microscope. Because it was not necessary to remove the microorganisms from the soil particles, it was possible to establish their occurrence in different microhabitats. This technique can provide useful ecological information about the soil microflora.     

Observation of individual DNA molecules undergoing gel electrophoresis

Individual DNA molecules undergoing agarose gel electrophoresis were viewed with the aid of a fluorescence microscope. Molecular shape and orientation were studied in both steady and pulsed electric fields. It was observed that (i) DNA macromolecules advanced lengthwise through the gel in an extended configuration, (ii) the molecules alternately contracted and lengthened as they moved, (iii) the molecules often became hooked around obstacles in a U-shape for extended periods, and (iv) the molecules displayed elasticity as they extended from both ends at once. A computer model has been developed that simulates the migration of the molecules in a rotating-field gel electrophoresis experiment.     

昆虫材料扫描电镜样品制备技术

在昆虫材料的扫描电镜样品制备中,组织固定是极其重要的环节.由于昆虫体壁均有一定程度的骨化,具有阻止外界物质侵入的作用,使得固定液不容易浸透昆虫体内组织器官,且昆虫体内液体含量较高,因此利用常规前固定方法（即用2％～3％的戊二醛固定）难以保持昆虫材料的原有形态.本研究通过改变固定液的配制方法,即在3％戊二醛中加入氯化钠及吐温-80,比较了桃蛀螟幼虫经过微波固定、常规固定和自然干燥标本处理后,在扫描电镜下的观察效果.结果发现：在微波和固定液共同处理下,昆虫材料扫描电镜样品皱缩程度显著降低,有益于观察昆虫体表的超微结构.研究结果可为昆虫扫描电镜材料的制备提供技术参考.     

Image-formation technique for scanning electron microscopy and electron probe microanalysis

A technique is described for topographic images on the scanning electron microscope and the scanning electron probe microanalyzer. In this technique, the brightness of the oscilloscope is modulated by a signal obtained by mixing the signal (from secondary electrons or targets current) with its first derivative. This enhances minor topographic features which are poorly reproduced in the technique.     

Scanning electron microscopy of developing plant organs

Shoot apices and young meristematic leaves can be examined directly with the scanning electron microscope without prior fixation or metal coating. The form of the shoot apex, cellular organization, andleaf arrangement (phyllotaxis) can be observed, perphaps as they have never been visualized before.     

High-resolution electron microscopy and scanning tunneling microscopy of native oxides on silicon

High-resolution transmission electron microscopy and scanning tunneling microscopy have been combined to examine the structure of the thin "native" oxide that forms on silicon surfaces at room temperature. Differences in the cleaning procedures for silicon wafers may affect the morphology of this oxide and critically influence further processing on the silicon substrates. An etch that ended with a dip in hydrofluoric acid provided a thinner oxide and a lower interface step density than did a sulfuric peroxide treatment. The availability of complementary information from high-resolution transmission electron microscopy and scanning tunneling microscopy is discussed.     

Single molecules observed by near-field scanning optical microscopy

Individual carbocyanine dye molecules in a sub-monolayer spread have been imaged with near-field scanning optical microscopy. Molecules can be repeatedly detected and spatially localized (to approximately lambda/50 where lambda is the wavelength of light) with a sensitivity of at least 0.005 molecules/(Hz)(1/2) and the orientation of each molecular dipole can be determined. This information is exploited to map the electric field distribution in the near-field aperture with molecular spatial resolution.     

Scanning electron microscopy of fresh leaves of pinguicula

Moist surfaces of leaves of Pinguicula grandiflora Lamck. can be observed directly by scanning electron microscopy, without metal coating. Samples dry out rapidly in the instrument, but during the first few minutes images can be obtained which must represent the natural state of the leaf surface.     

Scanning electron microscopy of the organ of Corti

With the scanning electron microscope we have examined normal cochlear sensory epithelium of the guinea pig and cat and that damaged by noise. The studies demonstrate how the regular surface architecture of the organ of Corti is altered after exposure to noise. The changes include loss of sensory hairs, formation of giant hairs, and complete degeneration of circumscribed areas of the organ of Corti. Our method greatly reduces the artifacts.     

Subliming ice surfaces: freeze-etch electron microscopy

Vacuum sublimation of oriented single crystals of ice at temperatures from -110 to -60 degrees Celsius was studied by electron microscopy with the freeze-etch technique. Sublimation etches the ice surface to produce pits and asperities and above -85 degrees Celsius causes extreme surface roughening. The etch pits are ascribed to surface dislocations, and the extreme roughening is ascribed to the departure from unity of the vaporization coefficient. The asperities could not be attributed to impurities; they may be related to the whiskers that others have observed at higher temperatures.     

Intramolecular long-distance electron transfer in organic molecules

Intramolecular long-distance electron transfer (EI) has been actively studied in recent years in order to test existing theories in a quantitative way and to provide the necessary constants for predicting ET rates from simple structural parameters. Theoretical predictions of an "inverted region," where increasing the driving force of the reaction will decrease its rate, have begun to be experimentally confirmed. A predicted nonlinear dependence of ET rates on the polarity of the solvent has also been confirmed. This work has implications for the design of efficient photochemical charge-separation devices. Other studies have been directed toward determining the distance dependence of ET reactions. Model studies on different series of compounds give similar distance dependences. When different stereochemical structures are compared, it becomes apparent that geometrical factors must be taken into account. Finally, the mechanism of coupling between donor and acceptor in weakly interacting systems has become of major importance. The theoretical and experimental evidence favors a model in which coupling is provided by the interaction with the orbitals of the intervening molecular fragments, although more experimental evidence is needed.     

Ultrathin carbon support films for electron microscopy

Carbon support films only 4 to 6 angstroms thick have been made for use in electron microscopy. The determination of their thickness is based on geometrical calculation, electron scattering measurements, and elemental microanalysis.     

Spot-scan imaging in transmission electron microscopy.

The determination of the structure of proteins and other organic materials by transmission electron microscopy is a rapidly developing field. Obtaining high-resolution images of these radiation-sensitive specimens has, until recently, been problematic. The development of spot-scan imaging, in which the electron beam is focused to a spot with a diameter of about 1000 angstroms and moved over the specimen to record the image, has overcome some of the most severe problems, which result from beam-induced motion of the specimen and its image. Elimination of this motion greatly enhances the contrast of high-resolution features of the image and promises a significant increase in the speed with which future structural work can be accomplished.