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31.
Optical tweezers (infrared laser-based optical traps) have emerged as a powerful tool in molecular and cell biology. However, their usefulness has been limited, particularly in vivo, by the potential for damage to specimens resulting from the trapping laser. Relatively little is known about the origin of this phenomenon. Here we employed a wavelength-tunable optical trap in which the microscope objective transmission was fully characterized throughout the near infrared, in conjunction with a sensitive, rotating bacterial cell assay. Single cells of Escherichia coli were tethered to a glass coverslip by means of a single flagellum: such cells rotate at rates proportional to their transmembrane proton potential (. J. Mol. Biol. 138:541-561). Monitoring the rotation rates of cells subjected to laser illumination permits a rapid and quantitative measure of their metabolic state. Employing this assay, we characterized photodamage throughout the near-infrared region favored for optical trapping (790-1064 nm). The action spectrum for photodamage exhibits minima at 830 and 970 nm, and maxima at 870 and 930 nm. Damage was reduced to background levels under anaerobic conditions, implicating oxygen in the photodamage pathway. The intensity dependence for photodamage was linear, supporting a single-photon process. These findings may help guide the selection of lasers and experimental protocols best suited for optical trapping work. 相似文献
32.
Phylogenetic profiles: a graphical method for detecting genetic recombinations in homologous sequences 总被引:13,自引:3,他引:10
Phylogenetic profiles constitute a novel way of graphically displaying the
coherence of the sequence relationships over the entire length of a set of
aligned homologous sequences. Using a sliding-window technique, this method
determines the pairwise distances of all sequences in the windows and
evaluates, for each sequence, the degree to which the patterns of distances
in these regions agree. This method is suited for exploring data
consistency as well as detecting recombinant sequences. A computer program
implementing the algorithm has been developed, and examples with simulated
and natural sequences are given to demonstrate the sensitivity and accuracy
of the method for identifying recombinant sequences and their recombination
junctions as well as detecting hot spots of recombinational activity.
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