Relationship between polyadenylated and nonpolyadenylated herpes simplex virus type 1 latency-associated transcripts.

RNA from the region of the genome encoding herpes simplex virus type 1 latency-associated transcripts (LATs) expressed during lytic infection yields low abundances of both polyadenylated and nonpolyadenylated forms. As has been previously shown for latent infection (A. T. Dobson, F. Sedarati, G. Devi-Rao, W. M. Flanagan, M. J. Farrell, J. G. Stevens, E. K. Wagner, and L. T. Feldman. J. Virol. 63:3844-3851, 1989), all lytic-phase expression of such transcripts requires promoter elements situated approximately 600 bases 5' of the previously mapped 5' end of the poly(A)- forms of LAT. Transient expression experiments revealed no other clear promoter elements within this region, and relatively small amounts of latent-phase transcripts initiating at the same site as observed for lytic-phase LAT could be detected by RNase protection assays. In the lytic phase of infection, the most abundant forms of polyadenylated LAT extended 1,600 bases from the initiation site near the LAT promoter to a potential splice donor site. Poly(A)- LAT species were not recovered in significant amounts from lytically infected neuroblastoma cells, but such RNA from lytically infected rabbit skin cells comapped with poly(A)- LAT from latently infected sensory neurons. Both map between canonical 5' splice donor and 3' splice acceptor site 1,950 bases apart. Poly(A)- LAT cochromatographed with uncapped rRNA on m-aminophenyl boronate agarose under conditions in which capped mRNA was bound. All of these data confirm the previously presented scheme for the expression of poly(A)- LAT as a stable intron derived from the splicing of a large primary transcript; however, we were unable to detect the spliced polyadenylated product of this splicing reaction.