Studies of Fowl Plague Virus Temperature-sensitive Mutants with Defects in Synthesis of Virion RNA

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Abstract
Three different types of impairment in the synthesis of virion RNA (vRNA) were detected in 3 groups of temperature-sensitive (ts) mutants of fowl plaque virus (FPV) having ts mutations in genes, 1, 3 and 5, respectively. Normal synthesis of poly(A+) c[complementary]RNA, poly(A-) cRNA and vRNA was observed under nonpermissive conditions early in infection in chicken embryo fibroblast cells infected with the ts 43 mutant having a ts mutation in gene 1 coding for the PB2 protein. However, 4 h after infection synthesis of vRNA ceased, synthesis of poly(A+) cRNA was reduced drastically, but the rate of poly(A-) cRNA synthesis was the same as that in cells infected with wild-type FPV. In cells infected with the ts 166 mutant having a ts mutation in gene 3, coding for the PA polypeptide, a drastic reduction was observed in poly(A+) cRNA synthesis under nonpermissive conditions. Synthesis of poly(A-) cRNA was also reduced and synthesis of vRNA was not detected. The ts 60 mutant, having a ts mutation in gene 5 coding for the NP polypeptide, induced synthesis of all types of virus-specific RNA under nonpermissive conditions, but the regulation of synthesis of vRNA and poly(A+) cRNA was affected, there being predominant synthesis of RNA segments 5 and 8 late in infection. In cells infected with mutants ts43 and ts 166 synthesis of virus-specific proteins was impaired, which reflected defects in the synthesis of virus-specific RNA. Evidently, the PB2 protein may be contained in an enzyme complexe responsible for synthesis of vRNA, different enzyme complexes may be involved in the synthesis of poly(A-) cRNA and vRNA and the NP protein plays a significant role in the regulation of vRNA synthesis.