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Mol. Cell. Biol., Jul 1995, 3864-3869, Vol 15, No. 7
ZM Huang and TS Yen
Hepatitis B virus S transcripts contain a region, known as the
posttranscriptional regulatory element (PRE), that activates their
transport from the nucleus to the cytoplasm. J. Huang and T. J. Liang (Mol.
Cell. Biol. 13:7476-7486, 1993) have shown that this element can partially
substitute for the human immunodeficiency virus Rev-response element (RRE)
in a reporter plasmid that is dependent on the RRE and Rev protein for
expression and concluded that PRE exhibits Rev-RRE-like functions by
inhibiting splicing. However, we have obtained additional data which
indicate that the PRE functions in a novel manner that is not dependent on
inhibition of splicing. Unlike Rev-RRE, the PRE functions independently of
splice donor and acceptor sites and can activate cytoplasmic expression of
an intronless (so-called prespliced) beta-globin transcript. Conversely, a
heterologous intron can substitute for the PRE in increasing cytoplasmic
expression of hepatitis B virus S transcripts. In addition, the host
nuclear factor, YL2 (p32), which enhances Rev-RRE function has no effect on
PRE- dependent gene expression. Since S transcripts are not normally known
to be spliced and since RNA splicing and cytoplasmic transport are tightly
linked processes in higher eucaryotic cells, we conclude that the PRE
functions in cis to allow the export of nuclear transcripts that do not
interact efficiently with the splicing pathway and hence are normally not
exported well from the nucleus. Such elements are critical for the life
cycle of viruses, such as hepatitis B virus, which undergo reverse
transcription during replication.
Copyright © 1995, American Society for Microbiology
Role of the hepatitis B virus posttranscriptional regulatory element in export of intronless transcripts
Department of Pathology, University of California, San Francisco, USA.
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