Regulatory activity of distal and core RNA elements in Tombusvirus subgenomic mRNA2 transcription.

Positive-strand RNA viruses that encode multiple cistrons often mediate expression of 3'-encoded open reading frames via RNA-templated transcription of subgenomic (sg) mRNAs. Tomato bushy stunt virus (TBSV) is a positive-strand RNA virus that transcribes two such sg mRNAs during infections. We have previously identified a distal element (DE), located approximately 1100 nucleotides upstream from the initiation site of sg mRNA2 transcription, part of which must base pair with a portion of a core element (CE), located just 5' to the initiation site, for efficient transcription to occur (Zhang, G., Slowinski, V., and White, K. A. (1999) RNA 5, 550-561). Here we have analyzed further this long distance RNA-RNA interaction and have investigated the regulatory roles of other subelements within the DE and CE. Our results indicate that (i) the functional base-pairing interaction between these elements occurs in the positive strand and that the interaction likely acts to properly position other subelements, (ii) two previously undefined subelements within the DE and CE are important and essential, respectively, for efficient sg mRNA2 accumulation, and (iii) the production of (-)-strand sg mRNA2 can be uncoupled from the synthesis of its (+)-strand complement. These data provide important insight into the mechanism of sg mRNA2 transcription.