Temporal regulation of herpes simplex virus type 1 UL24 mRNA expression via differential polyadenylation

Using Northern blot, primer extension, and S1 nuclease analyses of wild-type and deletion-containing herpes simplex type 1 viruses, we found that UL24 sequences are contained in six different transcripts that originate from three previously identified mRNA start sites. Thus, the six UL24 transcripts represent three different pairs of 5' coterminal mRNAs. Each transcript pair consists of a short species whose 3' end corresponds to a polyadenylation signal located just downstream of the UL24 open reading frame, and a longer species whose 3' end corresponds to a polyadenylation signal located downstream of the UL26 gene. Maximal accumulation of the short UL24 transcripts was at early times during infection, while accumulation of the longer species did not decrease at late times. Consistent with early kinetics, the short transcripts were less sensitive to drugs that inhibited viral DNA replication than the longer transcripts which exhibited leaky-late kinetics. Quantitative S1 nuclease analysis indicated that 3' ends corresponding to the UL24 polyadenylation site were significantly more abundant at early times than at late times. Thus, differential polyadenylation determines the kinetics of accumulation of different UL24 transcripts.