Modulation of ppp(A2'p)nA-dependent RNase by a temperature-sensitive mutant of vaccinia virus

Activation of the ppp(A2'p)nA (2-5A)-dependent RNase was investigated during the abortive infection of BSC40 cells by a temperature-sensitive mutant of vaccinia virus, ts22. At the nonpermissive temperature, ts22 has an abortive late phenotype. At the onset of late-viral-gene expression, viral mRNA is degraded and rRNA is cleaved into discrete fragments in the absence of prior interferon treatment (R. F. Pacha and R. C. Condit, J. Virol. 56:395-403, 1985). Concomitant with rRNA cleavage, an increase in 2-5A occurred late during infection. Discrete 18S- and 28S-rRNA degradation products from BSC40 cells infected with ts22 at the nonpermissive temperature comigrated in denaturing agarose gels with rRNA cleaved fragments produced by the activation of 2-5A-dependent RNase in uninfected cells transfected with exogenous 2-5A. An increase in 2-5A levels and a similar discrete and characteristic degradation of rRNA were observed in BSC40 cells infected with wild-type vaccinia virus in the presence of isatin-beta-thiosemicarbazone. The results show that the ts22 lesion and the action of isatin-beta-thiosemicarbazone may affect the same pathway, leading to the activation of latent 2-5A-dependent RNase and resulting in indiscriminate RNA degradation and inhibition of viral replication.