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netLibrary - eBook Summary Structure-based Drug Design by ...

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Another is the loss from the ends of the viral DNA of the original two base pairs that preceded the<br />

conserved 3'-CA.<br />

B. In Vitro Assays to Monitor Integrase Activity<br />

Page 87<br />

In contrast to the in vivo reaction, concerted integration in vitro of two HIV DNA ends into a target<br />

DNA molecule separated <strong>by</strong> a 5 base-pair stagger occurs very inefficiently. However, in vitro systems<br />

have been developed [6,7] using recombinant HIV integrase that have allowed the chemistry of the<br />

single-ended integration event to be studied in fine detail. It is possible and routine to use short, doublestranded<br />

synthetic oligonucleotides that mimic the viral ends to monitor the removal of two nucleotides<br />

from 3' ends (denoted 3' processing or cutting) and the subsequent insertion of one 3' processed DNA<br />

molecule into another (known as strand transfer or joining). Typical reactions are depicted in Figure 3.<br />

The stereochemical mechanism of 3' processing and strand transfer has been investigated using DNA<br />

substrates that incorporate phosphorothioate link-ages [8]. For both reactions, the introduced chiral<br />

centers are inverted in the products, implying that the reactions occur via a one-step in-line displacement<br />

mechanism rather than via a covalent intermediate.<br />

A third assay of integrase activity, termed disintegration, has more recently been developed [9] that<br />

monitors the apparent reversal of strand-<br />

Figure 3<br />

Reactions carried out <strong>by</strong> integrase in vitro, using short oligonucleotide substrates.<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_87.html [4/5/2004 4:54:38 PM]

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