Electron microscopy of the segmented RNA genome ofLa Crosse virus: absence of circular molecules.

The three species of single-stranded RNA present in La Crosse virus were examined in the electron microscope. Because large amounts of contaminating cellular DNA are copurified with the virus despite extensive attempts to purify the virus, it was necessary to use procedures that eliminated the bulk of this DNA before the viral RNA was analyzed. When this was done, the modal lengths of La Crosse virus RNA were 0.4, 2.0, and 3.1 mum. These lengths correspond well to their known molecular weights of 0.4 x 106, 1.8 x 106, and 2.9 x 106. Under the denaturing conditions used to permit complete spreading of these single-stranded RNA molecules, no single-stranded circular molecules are observed. Therefore, the circular nucleocapsids present in La Crosse virus and some other bunyaviruses do not appear to be due to convalent linkage of the ends of the RNA genome.