Selection of a nonconsensus branch point is influenced by an RNA stem-loop structure and is important to confer...

Herpes simplex virus type 1 latent infection in sensory neurons is characterized by the highly restricted transcription of viral genes. The latency-associated transcripts (LAT) family members are the only transcripts that can be identified in large amounts in latently infected cells. The most abundant LAT species is a 2-kb RNA that results from splicing of a rare primary transcript. Analysis of a LAT mutant virus (TB1) in cell culture revealed an aberrant splicing pattern and production of a stable small (0.95-kb) LAT intron. A panel of deletion constructs expressing truncated LAT in transiently transfected cells mapped the region influencing stability to the 3' end of the LAT intron. This region encompasses the branch point and a putative stable stem-loop hairpin structure immediately upstream of the splice acceptor consensus polypyrimidine tract. Mutagenic analysis of the sequence in this region confirmed our hypothesis that the stem-loop structure is important for efficient splicing by influencing the selection of a nonconsensus branch point. Changes in this structure correlate with changes in branch point selection and production of an unstable 2-kb LAT.