RNA Molecules Bound to the Folded Bacterial Genome Stabilize DNA Folds and Segregate Domains of Supercoiling
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Excerpt
The DNA of bacterial cells, gently isolated in the presence of appropriate concentrations of counterions, is folded in compact, nonviscous structures (Stonington and Pettijohn, 1971). The dimensions of the DNA containing particles, as calculated from their sedimentation properties (Stonington and Pettijohn, 1971; Worcel and Burgi, 1972) and as observed via the electron microscope (Pettijohn et al., 1973), are close to the dimensions of the bacterial nucleoid as seen in vivo. The molecular weight of the isolated DNA, estimated from sedimentation studies, is similar to that expected of the intact genome (Stonington and Pettijohn, 1971; Worcel and Burgi, 1972). These studies indicate that the isolated particles contain the unbroken bacterial chromosome, condensed in a conformation resembling, at least grossly, its state in the cell; we therefore refer to the particles as isolated nucleoids.
Two different forms of the nucleoid have been isolated-the membrane-associated nucleoid and the membrane-free nucleoid (Pettijohn et al.,
