Nucleic Acids Research, Vol 24, Issue 18 3635-3642, Copyright © 1996 by Oxford University Press
RW McKenzie and MD Brennan
All Drosophila alcohol dehydrogenase (Adh) genes sequenced to date contain
two small introns within the coding region. These are conserved in location
and, to some extent, in sequence between the various species analyzed. To
determine if these introns play a role in Adh gene expression, derivatives
of the Drosophila affinidisjuncta Adh gene lacking one or both introns were
constructed and analyzed by germline and transient transformation of
Drosophila melanogaster. Removal of both introns lowered expression,
whether measured by enzyme activity or by RNA levels. The decrease was seen
in both germline transformed and transiently transformed larvae, with the
effect being larger for germline transformants. Similar decreases
(averaging 5-fold) were also seen at the embryonic and adult stages for
germline transformants. Nuclear run-off transcription with nuclei from
germline transformed embryos indicated that the reduction in RNA levels is
due to decreased transcription. However, LacZ fusion constructs designed to
test for the presence of a classical enhancer in the introns provided no
evidence for such a mechanism. Removal of each intron individually resulted
in more complex phenotypes. The introns have smaller, additive effects on
expression in adults. In larvae, removal of the upstream intron
significantly increases RNA levels but modestly decreases enzyme activity.
Removal of the downstream intron lowers expression in both germline and
transiently transformed larvae, but also increases position effects in
germline transformants. Therefore, the small introns are clearly needed for
optimal transcription of this Adh gene, but multiple mechanisms are
involved.
ARTICLES
The two small introns of the Drosophila affinidisjuncta Adh gene are required for normal transcription
Department of Biochemistry, School of Medicine, University of Louisville, KY 40292, USA.
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