A 0.8-kilobase SacI DNA fragment in the distal 5'-noncoding region of the c-Ha-ras1 oncogene hybridized to high guanine X cytosine sites of herpes simplex virus type 1 (HSV-1) DNA restriction fragments. Nucleotide sequence comparisons localized one of these sites to the intergenic region of HSV between the immediate-early genes coding for IEmRNA-3 and IEmRNA-4/5 that has enhancer-type activity. We tested the possibility that the HSV-1 enhancer and the upstream c-Ha-ras1 SacI fragment were functionally related by assaying for the capacity of recombinant plasmids in which the HSV-1 enhancer replaced the oncogene 0.8-kilobase SacI fragment to transform NIH/3T3 cells. Deletion of the 0.8-kilobase SacI fragment abolished the biological activity of c-Ha-ras1, but its replacement by the HSV-1 enhancer fully restored it. These results confirm the enhancer properties of the HSV-1 immediate-early intergenic region and suggest that c-Ha-ras1 sequences contained within the 0.8-kilobase SacI fragment plays a role in the transcriptional activation of the oncogene
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