A poxvirus bidirectional promoter element with early/late and late functions

A novel bidirectional promoter element of fowlpox virus (FPV) was characterized by transcription analysis, transient expression assays, and recombinant virus construction. This promoter element contained an early/late and a late function in opposite orientation, all within 42 bp of the DNA sequence. The 42-bp sequence was sufficient to express two reporter genes simultaneously in a temporally regulated manner. Both early and late mRNA from the early/late promoter originated at the same TAAAT motif and lacked a long 5'poly(A) leader sequence. Late mRNA, initiated from a TAAAT motif of the oppositely oriented late promoter strand, had a leader sequence of approximately 26 bases. Sequence alignment of two strands of the bidirectional element showed that 28 of 42 bases matched. Because of its small and defined size as well as unique structure, this bidirectional promoter should prove to be an important tool in defining the sequences required for the temporal regulation of poxvirus genes.