TANDEM PLACEMENT OF A CORONAVIRUS PROMOTER RESULTS IN ENHANCED MESSENGER-RNA SYNTHESIS FROM THE DOWNSTREAM-MOST INITIATION SITE

Insertion of the 17-nucleotide promoter region for the bovine coronavi rus N gene as part of a 27-nucleotide cassette into the open reading f rame of a cloned synthetic defective-interfering (DI) RNA resulted in synthesis of subDI RNA transcripts from the replicating DI RNA genome. Duplicating and triplicating the promoter sequence in tandem caused a progressive increase in the efficiency of subgenomic mRNA synthesis d espite a concurrent decrease in the rate of DI RNA accumulation that w as not specific to the promoter sequences being added. Although initia tion of transcription (leader fusion) occurred at each of the three pr omoter sites in the tandem construct, almost all of the transcripts we re found as a product of the most downstream (3'-most on the genome) p romoter. These results show that enhancement of subgenomic mRNA synthe sis is a property that can reside within sequence situated near the pr omoter. A possible role for the plus strand in the downstream promoter choice is suggested. (C) 1996 Academic Press, Inc.