INSTABILITY OF FROG VIRUS-3 MESSENGER-RNA IN PRODUCTIVELY INFECTED-CELLS

Cloned DNA restriction fragments encoding representative frog virus 3 messages were used as probes to assess the stability of viral transcri pts in infected fathead minnow cells. Analysis of Northern blot hybrid ization profiles confirmed earlier findings and revealed that in infec ted cells the steady-state level of representative frog virus 3 (FV3) messages increased throughout the replication cycle. However, when act inomycin D was added at 4 hr after infection to block the synthesis of new transcripts, viral messages were observed to turn over rapidly, w ith half-lives of approximately 2 hr. These results indicate that vira l transcripts were not preferentially stabilized in FV3-infected cells and suggest that the high steady-state level of viral messages presen t at late times after infection was due to viral transcription outpaci ng message degradation. Moreover, the instability of viral messages ch allenges the suggestion that the terminal dyad symmetry (hairpin struc ture) observed in all frog virus 3 messages sequenced to date plays a role in transcript stability. (C) 1994 Academic Press, Inc.