Structure and expression of the vaccinia virus gene which prevents virus-induced breakdown of RNA.

Three noncomplementing vaccinia virus temperature-sensitive mutants, ts4, ts22, and ts23, exhibit an abortive late phenotype characterized by the simultaneous cessation of protein synthesis, the breakdown of rRNA and viral mRNA, and an increase in intracellular concentrations of 2'-5'-linked oligoadenylates late during infection at the nonpermissive temperature (R.F. Pacha and R.C. Condit, J. Virol. 56:395-403, 1985; R.J. Cohrs, R.C. Condit, R.F. Pacha, C.L. Thompson, and O.K. Sharma, J. Virol. 63:948-951, 1989). We have identified the virus gene affected by the abortive late mutants, determined its DNA sequence, and analyzed its transcription. The gene resides in the HindIII A DNA fragment, it has a predicted coding capacity of 57 kilodaltons, and it is transcribed both early and late during infection. The early transcript of the abortive late gene is unusual; it contains a 426-nucleotide 5' untranslated region, and it must be synthesized by transcription through an early transcription termination signal which is located in the middle of the gene in a hairpin loop structure. DNA sequence and transcription analysis of two flanking genes is also presented.