Mikhail A. Podyminogin

A novel endonuclease IV post-PCR genotyping system

Here we describe a novel endonuclease IV (Endo IV) based assay utilizing a substrate that mimics the abasic lesions that normally occur in double-stranded DNA. The three component substrate is characterized by single-stranded DNA target, an oligonucleotide probe, separated from a helper oligonucleotide by a one base gap. The oligonucleotide probe contains a non-fluorescent quencher at the 5′ end and fluorophore attached to the 3′ end through a special rigid linker. Fluorescence of the oligonucleotide probe is efficiently quenched by the interaction of terminal dye and quencher when not hybridized. Upon hybridization of the oligonucleotide probe and helper probe to their complementary target, the phosphodiester linkage between the rigid linker and the 3′ end of the probe is efficiently cleaved, generating a fluorescent signal. In this study, the use of the Endo IV assay as a post-PCR amplification detection system is demonstrated. High sensitivity and specificity are illustrated using single nucleotide polymorphism detection.

Synthesis, characterization, and application of substituted pyrazolopyrimidine nucleosides.

This unit describes, in detail, the preparation of 3-aminopropyl-substituted pyrazolo[3,4-d]pyrimidine analogs of the purines deoxyadenosine (dA) and deoxyguanosine (dG). Phosphoramidite reagents of these so-called aminopropyl-PPA and -PPG nucleosides (AP-PPA and AP-PPG, respectively) allow introduction of amino linkers into internal positions of synthetic DNA strands. Synthesis of suitably protected AP-PPA and AP-PPG phosphoramidites are described. The stepwise alkynylation, hydrogenation, selective protection, and phosphoramidite synthesis is similar for both the PPA and PPG analogs. To demonstrate the application of these reagents, a protocol is given in which a simple DNA strand is synthesized and conjugated to a lipophilic activated ester (dabcyl-SE) to form a stable amide linkage. Utility of this chemistry for preparing internally modified DNA conjugates is discussed.