PubMed · 8512691
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R L Neve. 1993. An improved method for preparing lambda ZAP II DNA.. https://pubmed.ncbi.nlm.nih.gov/8512691/
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The rate of cyclization of lambda DNA varies over more than 6 orders of magnitude, from 3.2 x 10(-7) s-1 to 2 s-1, in a Tris-EDTA buffer as a function of spermidine concentration. This variation is strictly correlated with the conformation of the chain. The highest rates are obtained when the chain is collapsed into a dense globular state. The effective concentration of the chain ends in the reaction is then 87 000-fold greater than in the random coil state. These results show that DNA globularity must be taken into account to understand biological processes involving intramolecular DNA-DNA interactions.
The conformational dynamics of individual, flexible polymers in steady shear flow were directly observed by the use of video fluorescence microscopy. The probability distribution for the molecular extension was determined as a function of shear rate, gamma;, for two different polymer relaxation times, tau. In contrast to the behavior in pure elongational flow, the average polymer extension in shear flow does not display a sharp coil-stretch transition. Large, aperiodic temporal fluctuations were observed, consistent with end-over-end tumbling of the molecule. The rate of these fluctuations (relative to the relaxation rate) increased as the Weissenberg number, gamma;tau, was increased.
mariner family transposons are widespread among eukaryotic organisms. These transposons are apparently horizontally transmitted among diverse eukaryotes and can also transpose in vitro in the absence of added cofactors. Here we show that transposons derived from the mariner element Himar1 can efficiently transpose in bacteria in vivo. We have developed simple transposition systems by using minitransposons, made up of short inverted repeats flanking antibiotic resistance markers. These elements can efficiently transpose after expression of transposase from an appropriate bacterial promoter. We found that transposition of mariner-based elements in Escherichia coli produces diverse insertion mutations in either a targeted plasmid or a chromosomal gene. With Himar1-derived transposons we were able to isolate phage-resistant mutants of both E. coli and Mycobacterium smegmatis. mariner-based transposons will provide valuable tools for mutagenesis and genetic manipulation of bacteria that currently lack well developed genetic systems.