Characterization of vaccinia virus transcripts involved in selective inhibition of host protein synthesis

Vaccinia virus transcripts synthesized in vitro inhibit protein synthesis directed by globin mRNA, EMC RNA, and total cytoplasmic RNA isolated from HeLa and CHO cells in micrococcal nuclease-treated reticulocyte lysates. In contrast, RNA isolated from vaccinia virus-infected cells is efficiently translated in the same system in the presence of the in vitro transcripts (G. Coppola and R. Bablanian (1983), Proc. Natl. Acad. Sci. USA 80, 75-79). In this study, we have fractionated the in vitro transcripts by acid-urea-agarose gel electrophoresis and demonstrated that the smallest RNA fraction inhibited translation of HeLa cell mRNA in vitro but had no effect on vaccinia virus mRNA translation. On the other hand, the larger RNA species inhibited nonselectively. These results indicate that the selective inhibitory activity of vaccinia virus transcripts resides only in the small poly(A)-containing in vitro RNA fraction.