After
infection of mouse L cells with mengovirus, there is a rapid inhibition of
protein synthesis, a concurrent disaggregation of polysomes, and an accumulation of 80S ribosomes. These 80S ribosomes could not be chased back into polysomes under an elongation block. The infected-cell 80S-ribosome fraction contained twice as much initiator methionyl-
tRNA and
mRNA as the analogous fraction from uninfected cells. Since the proportion of 80S ribosomes that were resistant to
pronase digestion also increased after
infection, these data suggest that the accumulated 80S ribosomes may be in the form of initiation complexes. The specific
protein synthetic activity of polysomal ribosomes also decreased with time of
infection. However, the transit times in mock-infected and infected cells remained the same. Cell-free translation systems from infected cells reflected the decreased
protein synthetic activity of intact cells. The addition of reticulocyte
initiation factors to such systems failed to relieve the inhibition. Fractionation of the infected-cell lysate revealed that the ribosomes were the predominant target affected. Washing the infected-cell ribosomes with 0.5 M KCI restored their translational activity. In turn, the
salt wash from infected-cell ribosomes inhibited translation in lysates from mock-infected cells. The inhibitor in the ribosomal
salt wash was temperature sensitive and
micrococcal nuclease resistant. A model is proposed wherein
virus infection activates (or induces the synthesis of) an inhibitor that binds to ribosomes and stops translation after the formation of the 80S-ribosome initiation complex but before elongation. The presence of such an inhibitor on ribosomes could prevent them from being remobilized into polysomes in the presence of an inhibitor of
polypeptide elongation.