Chemistry Reference
In-Depth Information
contrast, the results obtained by Ichikawa
20
and Mao
44
with Zn(II) complexes and
by Schneider
43
with Co(III) complexes bearing ammonium groups indicate that the
use of such affi nity elements may be much less demanding in terms of structural
requirements.
Short DNA oligonucleotides (for both antisense recognition and triple helix
formation) or PNA fragments are probably the most promising DNA-binding subu-
nits available to chemists. Indeed, such systems conjugate tight binding to DNA with
high selectivity, and such features are ideally suited for the obtainment of a truly
useful artifi cial nuclease. Such systems have been extensively studied for RNA
3b
but,
up to today, very few agents have been studied with DNA and they have only been
tested on short single strand fragments, while the problem of double-strand cleavage
of DNA has still to be addressed.
13.9 Conclusions
Since the fi rst report on the ability of metal ions to promote DNA hydrolysis, tre-
mendous progress toward the obtainment of effi cient synthetic DNA hydrolytic
agents has been attained. At present, chemists have at their disposal catalysts that
cleave DNA in a few tens of minutes and, in some cases, can display interesting
selectivity. However, several other aspects need to be addressed before a catalyst
may reach the stage of practical application. Among the most important are: selec-
tivity, double-strand scission and cleavage effi ciency. The last point is of particular
importance in the case of intrinsically less reactive, but biologically relevant metal
ions, such as, for example, Zn(II). The use of multinuclear complexes as catalysts
and of selective DNA-binding subunits supported by careful design of the system
appear to be the main routes that have been successfully followed to date. Now, the
problem is the integration of these different features into a single system in order
to obtain really effective metallonuclease models.
The Komiyama ARCUT system
5
outlines an alternative strategy to that fol-
lowed by the majority of the researchers in the fi eld. In this case, selective cleavage
of ssDNA over dsDNA has been exploited trough an extensive investigation of the
reactivity of a single, very simple, and even moderately effi cient cleaving agent. Such
selectivity, conjugated with a smart design for the working protocol, has led to the
realization of the only artifi cial restriction agent so far reported. Also in this case
higher reactivity would be desirable in order to achieve shorter reaction times and
higher cleavage yields, but the success obtained represents strong encouragement
toward a renewed research effort in this fi eld.
Acknowledgements
We are deeply indebted to Prof. Umberto Tonellato, Prof. Paolo Scrimin, Prof.
Manlio Palumbo, Dr Claudia Sissi and Prof. Stefano Moro for their productive col-
laboration and numerous stimulating discussions.
