Disruption of the 5' and 3' splice sites flanking the major latency-associated transcripts of herpes simplex virus type 1: evidence for alternate splicing in lytic and latent infections.

The herpes simplex virus type 1 (HSV-1) latency-associated transcripts (LATs) are the only viral gene products expressed within latently infected neurones. The most abundant (major) LATs consist of two collinear nuclear polyA- RNAs of 2 kb and 1.5 kb which it has been suggested represent stable introns derived from a less abundant primary transcript (minor LAT). Consistent with this proposition is the identification of consensus splice donor and acceptor sites flanking major LATs which are conserved between HSV types 1 and 2. Here we test the functionality of the predicted splice sites within the context of the virus genome during productive infection in vitro and latent infection in vivo. To this end viruses in which the LAT splicing signals were disrupted by site-directed mutagenesis were constructed. We report that mutation of the splice acceptor site abrogates 2 kb major LAT generation during productive infection but does not significantly influence major LAT synthesis during neuronal latency. Similarly, mutation of the splice donor site significantly reduces levels of 2 kb major LAT during productive infection but has no detectable effect on the generation of 2 kb major LAT during neuronal latency as assessed by Northern and in situ hybridization analyses of latently infected neuronal tissue. From these data it can be concluded that the proposed splice sites flanking the major LAT region are dispensable for 2 kb major LAT production in neurones latently infected with HSV-1 but constitute functional splicing signals in productively infected non-neuronal cells.