Volume 271, Number 39,
Issue of September 27, 1996
pp. 24187-24192
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.
Double Hairpin Complexes Allow Accommodation of All Four Base
Pairs in Triple Helices Containing Both DNA and RNA Strands
(Received for publication, March 5, 1996, and in revised form, June 17, 1996)
Emanuelle
Pascolo
and
Jean-Jacques
Toulmé
From the INSERM U.386, IFR Pathologies Infectieuses,
Université Victor Segalen Bordeaux II, 146 rue Léo Saignat,
33076 Bordeaux cédex, France
We investigated the binding of an antisense
oligodeoxynucleotide to a stem-loop structure corresponding to the
mini-exon sequence of the protozoan parasite Leishmania
amazonensis. This oligomer was designed to anneal to the
single-stranded region adjacent to the bottom of the hairpin and to
fold back on itself, giving rise to a ``double-hairpin'' complex that
involved a local triplex. This imposed the recognition, by the third
strand, of a ``purine'' strand containing 6 interspersed pyrimidines
out of 15 nucleic acid bases. The sequence of the complementary
oligonucleotide was derived from the so-called pyrimidine motif; the
third strand of the anti-mini-exon oligomer was parallel to the purine
strand of the target. Electrophoretic mobility shift assays and
footprinting studies demonstrated that such an antisense oligomer was
able to bind to both the DNA and RNA versions of the
Leishmania hairpin. These double hairpin complexes allowed
the formation at pH 6.0 of a triple-stranded structure, despite the
presence of 4 A:T*G and 2 G:C*T triplets out of 15.