Distinctive nucleotide sequences adjacent to multiple initiation and termination sites of an early vaccinia virus gene.

Poxviruses, unlike other DNA viruses, replicate in the cytoplasm of infected cells and use their own system of transcription. Examination on one early mRNA synthesized in vivo and in vitro indicated that it has multiple closely spaced 5' and 3' ends. A remarkable 88% AT-rich 60 bp DNA sequence was found immediately upstream of the initiation of transcription sites. Although DNA sequences that bear some homology to Pribnow and Hogness boxes are present, additional recognition sequences located further upstream of procaryotic and eucaryotic initiation sites are absent. A possible initiation of translation codon occurs about 50 nucleotides from the 5' end of the message. The transcript terminates near or within a hexanucleotide CTATTC that is tandemly repeated four times. Sequences similar to those regulating termination of transcription in procaryotes or poly (A) addition in eucaryotes were not found, suggesting that poxviruses have evolved unique recognition signals.