FIG 3.

US28 is expressed in hematopoietic progenitor cells during latent infection. To confirm US28 expression during latency, we infected Kasumi-3 cells or primary CD34⁺ cells under conditions favoring a latent infection. Following 18 days in culture, each cell subset was cultured for an additional 2 days under conditions favoring either latency, using Kasumi-3 cells without TPA (23) or CD34⁺ cells in human long-term culture medium (51), or lytic reactivation, using Kasumi-3 cells with TPA (23) or CD34⁺ cells in reactivation medium (51). Cells were then harvested for RNA isolation, and the ratio of cDNA expression of US28 to UL123 was assessed by RT-qPCR in triplicate. Under latent conditions, the ratio of US28/UL123 is high, suggesting that US28 is expressed while UL123 is repressed. However, the US28/UL123 ratio nears 1 upon reactivation as both of these genes are highly expressed during lytic replication. The latent transcript UL138, the early lytic transcript UL44, the late lytic transcript UL99, and an additional HCMV GPCR, US27, are also shown as controls. *, P < 0.001. AU, arbitrary units.