Knot, electron micrograph

Marine aerosols are sampled for dust and salt by impingement of the aerosol particles onto nylon meshes 12). This dust-kite method (13, 14) uses a mesh with a strand diameter of 230/x and an air speed of approximately 15 knots. High-speed aerosol collectors 12) used on ships and aircraft employ meshes with strands of 48/a diameter and an air speed of 75-150 knots. Electron micrographs show that dust particles of 0.1 are collected by these high-speed samplers. To collect condensates (rain and fog) aboard ship, we have modified the shape of a dust kite so that the condensates will run to one point on the bottom and drop directly into a 1-liter polyethylene bottle. The system has collected up to 500 ml/hour in a fog of 0.5-mile visibility. 

Figure 5-17 Electron micrograph of a six-noded knot made by the Tn3 resolvase which is involved in movement of the Tn3 transposon (Chapter 27) from one location to another within the genome. Putative six-noded knot DNA was isolated by electroelution from an agarose gel. The knots, which are nicked in one strand, were denatured to allow the nicked strand to slide away and leave a ssDNA knot. This was coated with E. coli rec A protein (Fig. 27-24) to greatly thicken the strand and to permit the sign of each node (designated in the tracing) to be seen. From Wasserman et a/.184...

Figure 8-34. Scanning electron micrograph of a knotted hair fiber, illnstrating the cnticle cell surface structure. Note the raised scales caused by the severe bending stress of the knotted fiber.

The winding of DNA in higher-order forms such as knots and catenanes was also shown in electron micrographs of DNA molecules coated with Escherichia coli RecA protdn. It was found that DNA topoisomerase I of E. coli generates an equal mixture of (+) and (-) duplex DNA knots, and that one product was a catenane. It was later shown that RecQ helicase and topoisomerase III (Topo III) of E. coli together mediate a potent DNA strand passage activity that can catenate covalendy dosed DNA." The structure of the catenated DNA spedes formed by... 

Fig. 12 Scanning electron micrographs of a knotted polyDCHD fibre.

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