The mechanism by which 5-formylcytosine (fC) is recognised by enzymes involved in epigenetic modification and reading of DNA is not known, and recently an unusual DNA structure (F-DNA) was proposed as the basis for enzyme recognition of clusters of fC. We used NMR and X-ray crystallography to compare several modified DNA duplexes with the unmodified analogues and show that in the crystal state they all belong to the A-family, but in solution they are all members of the B-family. Contrary to the previous study, we find that 5-formylcytosine does not significantly affect the structure of DNA, though there are modest local differences at the modification sites. Hence, global conformation changes are unlikely to account for the recognition of this modified base, and our structural data favour a mechanism that operates at base-pair resolution for the recognition of 5-formylcytosine by epigenome-modifying enzymes.

We report the use of Co-porphyrins as electrochemical tags for a highly sensitive and selective genosensor. An avian influenza virus-based DNA sequence characteristic of H5N1 was detected at femtomolar levels from competing non-complementary sequences through hybridisation with the labeled DNA.

In the field of nucleic acid therapy there is major interest in the development of libraries of DNA-reactive small molecules which are tethered to vectors that recognize and bind specific genes. This approach mimics enzymatic gene editors, such as ZFNs, TALENs and CRISPR-Cas, but overcomes the limitations imposed by the delivery of a large protein endonuclease which is required for DNA cleavage. Here, we introduce a chemistrybased DNA-cleavage system comprising an artificial metallonuclease (AMN) that oxidatively cuts DNA, and a triplex-forming oligonucleotide (TFO) that sequence-specifically recognises duplex DNA. The AMN-TFO hybrids coordinate Cu II ions to form chimeric catalytic complexes that are programmable-based on the TFO sequence employed-to bind and cut specific DNA sequences. Use of the alkyne-azide cycloaddition click reaction allows scalable and high-throughput generation of hybrid libraries that can be tuned for specific reactivity and gene-ofinterest knockout. As a first approach, we demonstrate targeted cleavage of purine-rich sequences, optimisation of the hybrid system to enhance stability, and discrimination between target and off-target sequences. Our results highlight the potential of this approach where the cutting unit, which mimics the endonuclease cleavage machinery, is directly bound to a TFO guide by click chemistry.