1. The sucrose-gradient pattern of 32P-labelled RNA synthesized in actinomycintreated baby-hamster kidney cells infected with foot-and-mouth-disease virus depends greatly on the period of labelling. 2. Fractions are formed in infected cells that sediment at 12–20s and have the same base composition as similar fractions found in non-infected cells that have been treated with actinomycin. 3. In the presence of guanidine, which completely inhibits viral RNA synthesis, these fractions are labelled to a greater extent than in non-infected cells.
