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Journal of Virology, December 1998, p. 9889-9896, Vol. 72, No. 12
Infectious Disease Laboratory, The Salk
Institute for Biological Studies, La Jolla, California 92037
Received 11 May 1998/Accepted 27 August 1998
Herpes simplex virus genes are predominantly intronless. We
identified cis-acting elements in the intronless herpes
simplex virus type 1 thymidine kinase (TK) gene that facilitate
intron-independent gene expression. TK sequences functionally replaced
the hepatitis B virus (HBV) posttranscriptional regulatory element
(PRE) by inducing the expression of the intronless HBV surface message. TK also activated the pDM138 assay by inducing the cytoplasmic accumulation of intron-containing RNA. Multiple cis-acting
RNA sequences, or subelements, that induce cytoplasmic localization of
unspliced RNA were mapped within the TK gene. The presence of multiple
RNA subelements within the TK gene is reminiscent of the multiple
subelements in the HBV PRE required for the cytoplasmic accumulation of
intronless HBV RNAs. Similar to HBV PRE subelements, duplication of a
single TK subelement resulted in greater-than-additive increases in
activity. A reporter chimera containing a single TK subelement
juxtaposed to an HBV PRE subelement demonstrated a commensurate
increase in activity. These results suggest that viral intronless genes
utilize a similar strategy for intron-independent gene expression that
requires multiple cis-acting RNA signals. Furthermore, like
HBV PRE-containing RNA, TK cytoplasmic localization is not sensitive to
leptomycin B, a drug that inhibits the export of proteins containing
nuclear export signals. From this, we conclude that proteins that bind
TK and facilitate its cytoplasmic accumulation do not travel through a
CRM1-dependent RNA transport pathway.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Splicing-Independent Expression of the Herpes
Simplex Virus Type 1 Thymidine Kinase Gene Is Mediated by Three
cis-Acting RNA Subelements
*
Corresponding author. Mailing address: The Salk
Institute for Biological Studies, Infectious Disease Laboratory, P.O.
Box 85800, La Jolla, CA 92037. Phone: (619) 453-4100, ext. 1559. Fax: (619) 554-0341. E-mail: Hope{at}salk.edu.
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