Electron microscopy of membrane-free folded chromosomes from Escherichia coli.

Membrane-free folded chromosomes were purified from log-phase cultures of Escherichia coli and prepared for electron microscopy by aqueous (Kleinschmidt and Zahn) spreading. The appearance of the chromosomes depended on the salt concentrations in spreading. At certain salt concentration, the chromosomes resembled rosettes, with supercoiled loops of DNA radiating from a central core containing RNA.

Electron microscopy of membrane-associated folded chromosomes of Escherichia coli.

Membrane-associated folded chromosomes were purified from log-phase cultures of Escherichia coli 15 TAU-bar and prepared for electron microscopy by aqueous spreading techniques. A spectrum of structures was observed, ranging from condensed structures with no DNA fibers visible, to extended structures with DNA fibers. In the extended structures, loops of DNA radiated from residual envelope, the loops sometimes appeared supercoiled, and both their number and apparent contour length approximated previous estimates from physical and biochemical data.

Genome-sized RNA from reovirus particles.

Spider-like forms of purified reovirus RNA have been characterized by electron microscopy. These structures contained 11.3 +/- 0.