The methionyl transfer RNAs of Rous sarcoma virus.

An average volume of 1.11 pl of a standard TMV suspension was microinjected into single cultured tobacco cells using a glass capillary microneedle. The volume of virus suspension injected was calculated from 20 microneedles. The average number of characteristic TMV particles (290–310 nm) delivered was determined by direct count of the particles on slotted EM grids. All cells produced crystalline virus inclusions when injected with 620 or more TMV particles. One of two cells was infected after injection with 310 TMV particles and only one of four cells became infected after injection of 72 particles. Cell injections at lower concentrations produced no signs infection. Injected cells producing crystalline inclusions (the criterion for infection) were infectious when assayed on Nicotiana glutinosa L. Uninoculated controls and cells bioassayed immediately after injection with the standard and lowest infectious concentration gave a negative assay.