Identification and partial characterization of a new (50 S) subviral particle in Mengo virus-infected L cells

Abstract

A previously undetected subviral particle has been found in Mengo virus-infected L cells by sucrose density gradient centrifugal analysis of cytoplasmic supernatants (S 20) prepared from cells after labeling with [ 3H]amino acids during the early to mid-log phase of virus production. The particle (designated the “50 S particle” from its position between the ribosomal subunits in the gradient), together with mature virions (150 S) and previously described 14 S particles (McGregor et al., 1975), can be recovered from the S 20 fraction by high-speed centrifugation. It contains no RNA and is composed of equimolar amounts of the polypeptides ϵ, α, and γ. The results of conventional pulse-chase experiments suggest that it may be a precursor in the assembly of Mengo virions, but more convincing evidence that this is the case was obtained from experiments in which the chase was carried out in the presence of cordycepin (3′-deoxyadenosine). In the presence of this inhibitor of viral RNA synthesis, there is a significant accumulation of 50 S particles, and when the inhibition in reversed, a quantitative transfer of radiolabel from 50 S particles to mature virions ensues. The recovery of 50 S particles (and of mature virions) from cell homogenates is strongly dependent upon the concentration of KCl in the suspending buffer; only trace amounts are recovered at concentrations of less than 60 m M, while maximum recovery is achieved at a concentration of 100 m M.