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J Biol Chem, Vol. 274, Issue 31, 21763-21768, July 30, 1999
Repairing the Sickle Cell Mutation
I. SPECIFIC COVALENT BINDING OF A PHOTOREACTIVE THIRD STRAND TO
THE MUTATED BASE PAIR
Steven
Broitman,
Olga
Amosova,
Nina G.
Dolinnaya, and
Jacques
R.
Fresco
From the Department of Molecular Biology, Princeton University,
Princeton, New Jersey 08544
A DNA third strand with a 3'-psoralen substituent
was designed to form a triplex with the sequence downstream of the
T·A mutant base pair of the human sickle cell -globin gene.
Triplex-mediated psoralen modification of the mutant T residue was
sought as an approach to gene repair. The 24-nucleotide purine-rich
target sequence switches from one strand to the other and has four
pyrimidine interruptions. Therefore, a third strand sequence favorable
to two triplex motifs was used, one parallel and the other antiparallel to it. To cope with the pyrimidine interruptions, which weaken third
strand binding, 5-methylcytosine and 5-propynyluracil were used in the
third strand. Further, a six residue "hook" complementary to an
overhang of a linear duplex target was added to the 5'-end of the third
strand via a T4 linker. In binding to the overhang by
Watson-Crick pairing, the hook facilitates triplex formation. This
third strand also binds specifically to the target within a supercoiled
plasmid. The psoralen moiety at the 3'-end of the third strand forms
photoadducts to the targeted T with high efficiency. Such monoadducts
are known to preferentially trigger reversion of the mutation by DNA
repair enzymes.
Copyright © 1999 by The American Society for Biochemistry and Molecular Biology, Inc.

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Copyright © 1999 by the American Society for Biochemistry and Molecular Biology.
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