Encephalomyocarditis virus infection of mouse plasmacytoma cells. II. Effect on host RNA synthesis and RNA polymerases.

The effect of encephalomyocarditis virus infection of MOPC 460 mouse plasmacytoma cells on host RNA synthesis and RNA polymerases was investigated. Consistent with work performed in other virus host systems, rates of RNA synthesis appeared to be inhibited in infected cells, whereas RNA degradation appeared normal. These results were further extended with isolated nuclei, in which distinct RNA polymerase activities could be studied under conditions where problems with RNA turnover and endogenous nucleotide pool sizes were insignificant. Endogenous nuclear RNA polymerase II activity was inhibited early postinfection and at 1 to 2 h prior to endogenous RNA polymerase I plus III activity. However, the solubilized enzymes were fully active with exogenous DNA as template. In fact, the levels of RNA polymerases I, II, and III, isolated from infected cells and nuclei, were indistinguishable from levels in uninfected cells and nuclei at each stage of their partial purification procedure. The chromatographic properties of the enzymes on DEAE-Sephadex were also unaltered. Furthermore, the RNA synthetic activity of these isolated enyzmes, or of nuclei isolated from uninfected cells, was resistant to extracts of nuclei or of cytoplasmic fractions from infected cells. These results are discussed in terms of a possible inhibition of RNA synthesis in vivo at the level of transcription initiation.