Identification of a human cytomegalovirus virus DNA segment that complements an adenovirus 5 immediate early mutant

Human cytomegalovirus (HCMV) complements adenovirus mutant dl312, which is completely defective for expression of the adenovirus immediate early E1a gene region, for lytic growth (Tevethia and Spector, 1984). This assay defines at least one HCMV function, activation of the transcription of adenovirus early genes in trans, that must be provided for dl312 replication in coinfected cells. We show here that trans-activation depended on the expression of one or more HCMV gene. Human embryonic lung cells were transfected with dl312 DNA-protein complex and either HCMV DNA or recombinant plasmids containing the adenovirus E1a gene region or HCMV (Towne strain) DNA fragments. Replication of dl312 occurred only in cells that received both DPC and either the E1a gene, HCMV DNA, or the XbaI-E HCMV DNA fragment (0.68 to 0.77 map units). In addition, we show that HCMV also complemented adenovirus mutant pm975 for growth in 0.2% serum. Since pm975 grows poorly in low concentrations of serum due to a defect in an E1a gene product, this assay identified a second HCMV E1a-like function.