Studies of fowl plague virus temperature-sensitive mutants with defects in transcription

Two fowl plague virus temperature-sensitive (ts) mutants belonging to different complementation groups were studied. Both were defective in the syntheses of unpolyadenylated complementary RNA [A(-)cRNA] and virus RNA (vRNA) at non-permissive temperature whereas primary transcription was unaffected. In addition, ts 29, in which the ts mutation is in gene 1 coding for polypeptide P3, has a defect in 'secondary' synthesis of mRNA at non-permissive temperature whereas inhibition of mRNA synthesis by ts 131, in which the ts mutation is in gene 2 coding for polypeptide P1, appeared to result from a defect in vRNA synthesis. These results indicate, therefore, that different enzymes are responsible for the syntheses of virus mRNAs and A(-)cRNAs, which is consistent with the apparent differences in initiation and termination of transcription in the two reactions. The patterns of synthesis of the various types of virus RNA during infection are discussed.