The kinetics of the renaturation of Escherichia coli DNA in 0.4-1.0m-sodium chloride at temperatures from 60 degrees to 90 degrees have been studied. The extent of renaturation was a maximum at 65 degrees to 75 degrees and increased with ionic strength, and the rate constant increased with both ionic strength and temperature. The energy and entropy of activation of renaturation were calculated to be 6-7kcal.mole(-1) and -40cal.deg.(-1)mole(-1) respectively. It has been shown that renaturation is a second-order process for 5hr. under most conditions. The results are consistent with a reaction in which the rate-controlling step is the diffusion together of two separated complementary DNA strands and the formation of a nucleus of base pairs between them. The kinetics of the renaturation of T7-phage DNA and Bordetella pertussis DNA have also been studied, and their rates of renaturation related quantitatively to the relative heterogeneity of the DNA samples. By analysis of the spectra of DNA at different stages during renaturation it was shown that initially the renatured DNA was rich in guanine-cytosine base pairs and non-random in base sequence, but that, as equilibrium was approached, the renatured DNA gradually resembled native DNA more closely. The rate constant for the renaturation of guanine-cytosine base pairs was slightly higher than for adenine-thymine base pairs.
SUMMARYExamination of threads of Mycoplasma mycoides var. mycoides by optical and electron microscopy revealed organisms within a homogeneous mucinous matrix. This matrix stained with the periodic acid-Schiff (PAS) reagent method was almost electron-transparent and was probably lipo-polysaccharide (galactan) material. Treatment of threads with specific antibody produced a clearly visible microscopic precipitate strongly outlining the threads. By electron microscopy this precipitate was electron-dense, homogeneous, and finely granular ; it could frequently be seen surrounding individual mycoplasma cells as a well-defined capsule.
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