2.2-kilobase class of early transcripts encoded by cell-related sequences in human cytomegalovirus strain AD169.

In this report we describe the kinetics of appearance and fine mapping of a 2.2-kilobase (kb) class of transcripts arising from a region of the human cytomegalovirus genome which contains cell-related sequences. These transcripts are encoded by adjacent EcoRI fragments R and d (map units 0.682 to 0.713), located within the long unique segment of the genome. The 2.2-kb RNAs were first detected at 8h postinfection and appeared at comparable or slightly lower levels at 28 and 72 h postinfection. At late times (72 h) additional transcripts were detected with probes from this region. RNase, S1 nuclease, and exonuclease VII protection analyses of 8- and 28-h RNA indicated that the 2.2-kb RNAs had a complex spliced structure consisting of invariable 5' and internal exons and a heterogeneous 3' exon. The position of the 5' end of the RNA was determined with respect to the nucleotide sequence. Analysis of this sequence showed that the cell-related sequences were contained within a long open reading frame in the 5' exon.