Transcription of the human cytomegalovirus genome in productively infected cells.

Nuclear and cytoplasmic RNAs, synthesized in cells productively infected with human cytomegalovirus (HCMV) were analysed at various times after infection by liquid and filter DNA-RNA hybridization. Results of these experiments have revealed that: (i) the fraction of the genome transcribed increased as infection progressed. In the nucleus, transcripts represented approx. 20% of the virus DNA sequences at both 2 and 4 h post-infection (p.i.) and 36% of the virus DNA at 40 h p.i; (ii) the increase in virus sequences among nuclear transcripts at late times was prevented by the DNA synthesis inhibitor, 2'-deoxyfluorouridine; (iii) early virus RNA transcripts were subset of those represented in late RNA; (iv) two classes of early RNA were identified by competition hybridization; (v) approx. 10% of the late nuclear transcripts were symmetrical. Results of filter hybridization at DNA excess indicated that virus-specific RNA represented 0.6% of RNA labelled from 0 to 2 h p.i., and 1.8% of RNA labelled from 28 to 30 h. Polyadenylated RNA isolated from cytoplasm represented 1.2% and 10% of labelled mRNA at 2 h and 30 h respectively. Our data show that during productive infection of human cells by HCMV, gene expression is under temporal, quantitative and post-transcriptional control.