Polypurine reverse-Hoogsteen hairpin

The two polypurine domains interact by intramolecular reverse-Hoogsteen bonds allowing the formation of this specific hairpin structure.

PPRHs present high stability in serum and cells and show lack of immunogenicity not activating the innate inflammatory response.

Their action has been demonstrated in vitro for a number of genes involved in metabolism (DHFR), proliferation (mTOR), DNA topology (TOP1), lifespan and senescence (telomerase), apoptosis (survivin, BCL2), transcription factors and non-druggable targets (c-MYC[7] and k-Ras[8]) , proto-oncogenes (MDM2),[9] replication stress (WEE1, CHK1)[10] and Thymidilate synthase (TYMS)[11] as part of a cancer gene therapy strategy.

[14][15] PPRHs can also be used as the capture probe in different devises to detect viral infection by forming a triplex with the RNA of the virus such as SARS-CoV-2 in a technology termed Triplex Enhanced Nucleic Acid Detection Assay (TENADA)[16] PPRHs can be designed for virtually any gene in the genome by searching for polypirimidine stretches in the sequence of the desired gene.

Integrative WEB tools for identification and analysis of the triplex formation target DNA sequences, including PPRH sequences, associated with genes and regulatory elements (e.g., transcription factor binding sites, repeats, G-quadruplet motifs, SNPs, and non-protein coding regulatory DNA elements) in the human genome are publicly available (see External links).