FIG. 3.
Subgenomic templates designed to exclusively transcribe readthrough RNAs. Subgenomic templates having tetranucleotide sequences composed of A and U residues (the A/U group) (A) and templates having tetranucleotide sequences composed of G and C residues (the G/C group) (B) were constructed and used to generate metabolically labeled and actinomycin D-resistant RNAs in BHK cells as described in Materials and Methods. RNAs were visualized by agarose-urea gel electrophoresis and fluorography. The altered tetranucleotide sequences (negative sense, 3′-5′) of templates are shown above the lanes in which the corresponding RNAs products were electrophoresed. For reference, the wild-type termination sequence is shown, with the tetranucleotide sequence underlined. RNAs transcribed from subgenomic templates with tetranucleotide sequences AUAC (wild type) and AAAC, are shown alongside to indicate the mobility of terminated and readthrough RNAs. All tetranucleotide alterations within the A/U and G/C groups resulted in templates that directed exclusive synthesis of readthrough RNAs. In contrast to RNAs electrophoresed in Fig. 2B, the RNAs were not digested with RNase H.