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Mol. Cell. Biol., Aug 1997, 4372-4380, Vol 17, No. 8
A Furger, N Schurch, U Kurath and I Roditi
Procyclins are the major surface glycoproteins of insect forms of
Trypanosoma brucei. We have previously shown that a conserved 16-mer in the
3' untranslated region (UTR) of procyclin transcripts functions as a
positive element in procyclic-form trypanosomes. A systematic analysis of
the entire 297-base 3' UTR has now revealed additional elements which are
involved in posttranscriptional regulation: a positive element which
requires the first 40 bases of the 3' UTR and at least one negative element
between nucleotides 101 and 173 (the LII domain). Deletion of either
positive element resulted in a >8-fold reduction in the amount of
protein but only an approximately 2-fold decrease in the steady-state level
of mRNA, suggesting that regulation also occurred at the level of
translation. In contrast, deletion of LII caused a threefold increase in
the steady-state levels of both the mRNA and protein. LII-16-mer double
deletions also gave high levels of expression, suggesting that the 16-mer
functions as an antirepressor of the negative element rather than as an
independent activator. All three elements have an effect on RNA turnover.
When either positive element was deleted, the half-life (t(1/2)) of the
mRNA was reduced from approximately 50 min (the t(1/2) of the wild-type 3'
UTR) to < 15 min, whereas removal of the LII element resulted in an
increased t(1/2) of approximately 100 min. We present a model of
posttranscriptional regulation in which the negative domain is counteracted
by two positive elements which shield it from nucleases and/or
translational repressors.
Copyright © 1997, American Society for Microbiology
Elements in the 3' untranslated region of procyclin mRNA regulate expression in insect forms of Trypanosoma brucei by modulating RNA stability and translation
Institut fur Allgemeine Mikrobiologie, Universitat Bern, Switzerland.
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