Nadja Heidrich and Sabine Brantl @,
Institut für Molekularbiologie, Friedrich-Schiller-Universität Jena, Winzerlaer Straße, 10, Jena D-07745, Germany
@ E-mail: sabine.brantl@rz.uni-jena.de
Antisense-RNA mediated gene regulation has been found and studied in detail mainly in prokaryotic accessory DNA elements. In spite of different regulatory mechanisms, in all cases a rapid interaction between antisense and target RNA has been shown to be crucial for efficient regulation. Recently, a sequence comparison revealed in 45 antisense RNA control systems a 5' YUNR motif indicative for the formation of a U-turn structure in either an antisense or a target RNA loop and confirmed in the case of the hok/sok system of plasmid R1 its importance for regulation.
Here, we demonstrate the importance of the 5' YUNR motif in the target
RNA (RNAII) loop L1 of the replication control system of plasmid pIP501.
The effect of four individual mutations in L1 was studied in vivo
and in vitro. Mutations that maintained the putative U-turn or swapped
it from sense to antisense RNA were silent, whereas mutations that eliminated
the 5'-YUNR motif showed two- to threefold elevated copy numbers in
vivo in correlation with three- to fourfold reduced inhibition rate
constants of the complementary RNAIII species in vitro, whereas
the half-lives of all RNAIII species were not affected. ENU probing experiments
confirmed the U-turn structure for the silent mutation (N-C) and disruption
of this structure upon alteration of the invariant U or inversion of the
YUNR motif-containing loop. RNA secondary structure probing excluded loop
size alterations as a reason for altered inhibition rates. Implications
for the pathway and efficiency of
RNAII/RNAIII interaction, and hence, pIP501 copy-number control,
are discussed.
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and Slide Presentation.
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euchromatin: "the most active portion of the genome within the cell nucleus".