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J. Virol., Jan 1998, 225-235, Vol 72, No. 1
W Huang and SJ Flint
The subgroup C human adenoviruses induce selective export of newly
synthesized viral mRNA from the nucleus to the cytoplasm, with concomitant
inhibition of export of the majority of cellular mRNA species. Such
posttranscriptional regulation of viral and cellular gene expression in
infected cells requires viral E1B and E4 proteins. To facilitate the
investigation of parameters that govern selective export in
adenovirus-infected cells, we constructed a marked human beta-actin
minigene under the control of the glucocorticoid-inducible enhancer-
promoter of mouse mammary tumor virus and introduced it into the left end
of the adenovirus type 5 (Ad5) genome. Transcription of this reporter gene
(designated MA) as well as of a sibling, which differed only in the
inclusion of a cDNA copy of the Ad2 major late tripartite leader sequence
upstream of beta-actin sequences (termed MtplA), in recombinant
virus-infected cells was strictly dependent on the addition of
dexamethasone to the medium. When transcription of the MA gene was induced
during the late phase of infection, newly synthesized MA RNA entered the
cytoplasm. These transcripts, which contain no viral sequences, therefore
reproduce the behavior of exceptional cellular mRNA species observed when
transcription of their genes is activated during the late phase of
infection (U.-C. Yang, W. Huang, and S. J. Flint, J. Virol. 70:4071-4080,
1996). Unexpectedly, however, higher concentrations of newly synthesized
RNA accumulated in the cytoplasm when the tripartite leader sequence was
present in the reporter RNA, despite equal rates of transcription of the
two reporter genes. Examination of the partitioning of both newly
synthesized and steady- state populations of MA and MtplA RNAs between
nuclear and cytoplasmic compartments indicated that the tripartite leader
sequence did not increase RNA stability in the cytoplasm. Comparison of
nuclear and cytoplasmic reporter RNA species by Northern blotting, primer
extension, and reverse transcription-PCR provided no evidence for altered
processing induced by the tripartite leader sequence. We therefore conclude
that the tripartite leader sequence, long known to facilitate the
translation of mRNAs during the late phase of adenovirus infection, can
also modulate mRNA export from the nucleus.
Copyright © 1998, American Society for Microbiology
The tripartite leader sequence of subgroup C adenovirus major late mRNAs can increase the efficiency of mRNA export
Department of Molecular Biology, Princeton University, New Jersey 08544, USA.
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