Abstract
Tobacco mosaic virus RNA molecules were deposited as extended, oriented, single polynucleotide chains on carbon films for electron microscopy. This was accomplished by heating their solution to 45°C in the presence of formaldehyde, and then cooling rapidly to obtain a non-hydrogen bonded, random coil configuration at room temperature. Carbon films mounted on electron microscope grids were then streaked across the surface of the solution. The length distribution indicates that most of the molecules were either unbroken or suffered only one break. From the known molecular weight the base spacing is calculated to be between 6 and 7 Å. This is sufficient for an electron microscopic determination of their sequence using present instruments and adequately small nucleotide specific markers. The results suggest that the molecular weights of single polynucleotide chains can be determined by direct measurement of their length.
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