Electron Microscopy of Cells Infected with Semliki Forest Virus Temperature-Sensitive Mutants: Correlation of Ultrastructural and Physiological Observations

Cells infected at the permissive temperature with three temperature-sensitive mutants of Semliki Forest virus were not significantly different in appearance from cells infected, at either the permissive or nonpermissive temperature, with wild-type virus. Virus particles, nucleocapsids, spherules, and tubules were seen in the cytoplasm. But replication of the mutants was inhibited in cells infected at the nonpermissive temperature. This was evidenced by the absence of virus particles and nucleocapsids (except in one case) and the absence or limited production of spherules and tubules. These observations are discussed with reference to the physiological defects of the mutants.