Mapping of a major early/late gene of fowlpox virus

Identification, cloning and mapping of a major gene expressed during the early and late stages of infection with fowlpox virus is described. The gene is located within a 17.3 kb PstI fragment of the fowlpox virus genome and has an open reading frame of 501 bp. Analysis of the 5'-ends of mRNA transcribed from this gene showed that the start sites of both early and late transcripts map to the sequence TAAAT near the translation start site (ATG). This is the first poxvirus early/late gene described in which both early and late transcription start sites map to same DNA sequence. From northern hybridization analysis it was shown that the early function of this gene gives rise to the most abundant early mRNA coded by 17% of the fowlpox virus genome. The strong early function of this gene promoter will be useful in the construction of recombinant fowlpox viruses.