Fine mapping of transcripts expressed from the US6 gene family of human cytomegalovirus strain AD169.

By sequence analysis (K. Weston and B. G. Barrell, J. Mol. Biol. 192:177-208, 1986), the human cytomegalovirus (HCMV) strain AD169 HindIII X DNA fragment contains six open reading frames (US6 through US11; called the US6 family) which may encode glycoproteins. Sense transcripts from the US6 family were mapped. The kinetics of appearance of steady-state cytoplasmic RNA was different for each transcription unit. The 1.5-kb US11-US10 and the 1.7-kb US9-US8 transcripts belonged to the early kinetic class. The former reached peak abundance by 8 h postinfection, while the latter peaked at 24 h postinfection. These RNAs greatly decreased in abundance by 48 to 72 h after infection, unlike transcripts from other HCMV early transcription units reported previously. US6 and US7 messages were most abundant at late times postinfection. US6 transcripts utilized different initiation sites at early or late times postinfection. There was evidence for both spliced and unspliced messages from this family. In a transient expression assay, chimeric plasmids containing the regions upstream of the mapped transcription initiation sites were active in promoting indicator gene expression in HCMV-infected, but not uninfected, human foreskin fibroblast cells.