106
AIDS/HIV, Molecular and Cell Biology
5
3
3
5
5
5
5
5
5
5
5
5
3
3
Incoming provirus
Target cellular DNA
Fig. 6
Integration process.
cleavage and the viral and cellular DNA
ends are linked. Cellular enzymes fll in
the deFect (±ig. 6). The resulting sequence
shows a reduplication oF the cellular nu-
cleotides at either end oF the provirus.
The integrated provirus may remain
transcriptionally silent. Transcriptional ac-
tivation depends in part on the degree oF
stimulation oF the cell. In T cells, For ex-
ample, mitotic stimulation is associated
with activation oF the retroviral promoter.
Viral latency is a useFul strategy For this
pathogen to escape immune recognition
and studies suggest that, at any one time,
probably less than 10% oF inFected cells
have a transcriptionally active virus.
The 5
0
long terminal repeat oF the virus
contains a promoter element with a con-
ventional TATA box. When activated, this
is transcribed by RNA polymerase II to
produce a genome length transcript. Mul-
tiple small abortive transcripts are seen
early on but suFfcient Full-length RNAs
are produced to initiate gene expression.
Instability sequences are Found in the
Full-length RNA, which deFault the RNA
transcript to be spliced, and intronic se-
quences encompassing the Gag and Pol
regions and the central part oF envelope
are spliced out to produce multiply spliced
RNAs that are then exported into the cyto-
plasm and translated on Free cytoplasmic
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