Properties and growth mechanism of the ordered aggregation of a model RNA by the HIV-1 nucleocapsid protein: an electron microscopy investigation.

NCp7, the nucleocapsid protein of the human immunodeficiency virus type 1, induces an ordered aggregation of RNAs, a mechanism that is thought to be involved in the NCp7-induced promotion of nucleic acid annealing. To further investigate this aggregation the morphology and the properties of the NCp7-induced aggregates of the model RNA homoribopolymer, polyA, were investigated by electron microscopy in various conditions. In almost all the tested conditions, the aggregates were spherical and consisted of a central dense core surrounded by a less dense halo made of NCp7-covered polyA molecules.

Electron microscopy of the nucleocapsid from disrupted Moloney murine leukemia virus and of associated type VI collagen-like filaments.

To analyze the constituents of retroviruses, the Moloney murine leukemia virus was disrupted and observed by dark-field electron microscopy. Virus disruption was achieved by several methods: osmotic shock, freezing-thawing cycles, and exposure to urea up to 4 M, to NaCl up to 1 M, and to Triton X-100. Several components associated with broken Moloney murine leukemia virus were repeatedly found in preparations.

Homologous DNA targeting with RecA protein-coated short DNA probes and electron microscope mapping on linear duplex molecules.

We demonstrate that RecA protein-coated, short single-stranded DNA probes paired with a specific homologous DNA sequence in a linear duplex target molecule and accurately targeted the selected DNA sequence. RecA protein-coated complementary ssDNA probes were reacted with linear duplexes, and the homologously paired molecules were observed by electron microscopy. The sites of interaction between the RecA protein-coated DNA probes and the uncoated duplex DNA targets were directly visible on individual target DNA molecules by high-resolution darkfield electron microscopy, without chemical fixation or sample shadowing.