Macromolecular synthesis in cells infected by frog virus 3. XI. A ts mutant of frog virus 3 that is defective in late transcription.

Abstract

Abstract A ts mutant (ts 9467) of frog virus 3 (FV3) does not synthesize late viral RNAs or proteins, although it does synthesize viral DNA. We have analyzed by polyacrylamide gel electrophoresis the RNAs and proteins produced in ts 9467-infected cells to determine the requirements for turning on late transcription. The electrophoretic pattern of the mutant viral RNA species late in infection at 30° (nonpermissive temperature) was identical to the early RNA pattern seen during infection with wild-type virus. Temperature-shift experiments indicated that continuous viral protein synthesis was necessary for late transcription. The proteins produced by this mutant at 30° were similar to the early proteins in cells infected with wild-type FV3, with the exception of the appearance of a 38,000 MW protein. Although there was also a late protein with an identical molecular weight, this particular protein was synthesized in ts 9467-infected cells in the presence of fluorophenylalanine, an amino acid analog known to inhibit the formation of late FV3 RNAs and proteins. We postulate that this protein is an early protein not normally synthesized in detectable amounts, and that it may be the temperature-sensitive protein involved in late transcription. These studies conclusively demonstrate that (1) a virus-specific protein is required for late transcrip ion and (2) viral DNA synthesis per se is insufficient for the synthesis of late viral mRNAs and proteins.