Structure and regulation of the immediate-early frog virus 3 gene that encodes ICR489.

To test whether the promoters of two immediate-early genes from frog virus 3 were similar in nucleotide sequence, we have cloned and sequenced an immediate-early gene encoding an infected-cell mRNA of 489 kilodaltons (ICR489) and have shown that the protein product of this gene is approximately 46 kilodaltons. The 5' and 3' ends of the transcripts from this gene, as determined by mung bean nuclease analysis, were microheterogeneous. The promoter region was subcloned upstream from a promoterless chloramphenicol acetyltransferase gene, forming the recombinant plasmid pBS489CAT. As with the previously sequenced frog virus 3 immediate-early gene encoding ICR169, expression of chloramphenicol acetyltransferase in transfected cells required activation by a virion-associated protein. Although the promoter region of the gene encoding ICR489 contained TATA, CAAT, and GC motifs similar to those of typical eucaryotic promoters, it showed no significant homology to the ICR169 promoter, indicating that the concomitant temporal expression of these two genes is not due to similar promoter sequences.