Arch Virol (1999) 144: 381–391
Analysis of the latency-associated transcript/UL1-3.5 gene cluster
promoter complex of pseudorabies virus
A. K. Cheung and T. A. Smith
Virology Swine Research Unit, National Animal Disease Center, USDA,
Agricultural Research Service, Ames, Iowa, U.S.A.
Accepted September 8, 1998
Summary. During latency, pseudorabies virus (PRV) DNA is preferentially re-
tained in the neurons of the trigeminal ganglion and a spliced 8.5-kilobase poly-A
RNA, designated large latency transcript (LLT), is synthesized. Because LLT is
the only transcript made during the latent phase, the LLT promoter may be unique
among all other PRV promoters that are active in productive infections. Organi-
zation of the PRV LLT promoter is quite complex because it coincides with the
UL1-3.5 gene cluster promoter, but in the opposite orientation. By conventional
designation, LLT is transcribed in the rightward direction while the UL1-3.5 gene
cluster is transcribed in the leftward orientation. In this work, activities of the LLT
promoter and the UL1-3.5 gene cluster promoter were investigated by transient
reporter gene expression assay in cells of neuronal and non-neuronal origins.
There are two TATA boxes in this region. We examined the promoter activities of
the ﬁrst TATA box with its 5
sequence (LAP1) and the second TATA box with its
sequence (LAP2). The UL1-3.5 promoter driven constructs gave no reporter
gene activity in any of the experiments. Reporter gene activity was detected with
LAP2 gene constructs, but not with LAP1 constructs, in both neuronal and non-
neuronal cells. This is surprising because transcription of PRV LLT in vivo has
been attributed to LAP1 and the initiation site was mapped downstream of the
LAP1 TATA box and upstream of the LAP2 TATA box. Although LAP1 was not
active in these experiments, there was a 3- to 10-fold enhancement of activity
when LAP1 and LAP2 were placed in tandem.
Present address: Hach Company, Ames, IA 50010, U.S.A.