Biosynthesis and replication, from A to Z: Four nucleobases. adenine (A), cytosine (C), guanine (G), and thymine (T), are usually thought to be invariable in DNA. In bacterial viruses, however, each of the DNA bases have variations that help them to escape degradation by bacterial restriction enzymes. In the genome of cyanophage S-2L, A is completely replaced by diaminopurine (Z), which forms three hydrogen bonds with T and thus creates non–Watson-Crick base pairing in the DNA of this virus (see the Perspective by Grome and Isaacs). Zhou et al. and Sleiman et al. determined the biochemical pathway that produces Z, which revealed more Z genomes in viruses hosted in bacteria distributed widely in the environment and phylogeny. Pezo et al. identified a DNA polymerase that incorporates Z into DNA while rejecting A. These findings enrich our understanding of biodiversity and expand the genetic palette for synthetic biology. Science , this issue p. 512 , 516 , 520 ; see also p. 460

A straightforward route to original imidazole-based nucleosides that makes use of an enzymatic N-transglycosylation step is reported in both the ribo- and deoxyribo-series. To illustrate the scope of this approach, a diverse set of 4-aryl and 4-heteroaryl-1H-imidazoles featuring variable sizes and hydrogen-bonding patterns was prepared using a microwave-assisted Suzuki–Miyaura cross-coupling reaction. These imidazole derivatives were examined as possible substrates for the nucleoside 2′-deoxyribosyltransferase from L. leichmannii and the purine nucleoside phosphorylase from E. coli. The optimum transglycosylation conditions, including the use of co-adjuvants to address solubility issues, were defined. Enzymatic conversion of 4-(hetero)arylimidazoles to 2′-deoxyribo- or ribo-nucleosides proceeded in good to high conversion yields, except bulky hydrophobic imidazole derivatives. Nucleoside deoxyribosyltransferase of class II was found to convert the widest range of functionalized imidazoles into 2′-deoxyribonucleosides and was even capable of bis-glycosylating certain heterocyclic substrates. Our findings should enable chemoenzymatic access to a large diversity of flexible nucleoside analogues as molecular probes, drug candidates and original building blocks for synthetic biology.

Association of the initiation factor eIF4E with the mRNA cap structure is a key step for translation. Trypanosomatids present six eIF4E homologues, showing a low conservation and also differing significantly from the IF4Es of multicellular eukaryotes. On the mRNA side, while in most eukaryotes the mRNA contains cap-0 (7-methyl-GTP), the trypanosomatid mRNA features a cap-4, which is formed by a cap-0, followed by the AACU sequence containing 2′-O-ribose methylations and base methylations on nucleotides 1 and 4. The studies on eIF4E-cap-4 interaction have been hindered by the difficulty to synthesize this rather elaborated cap-4 sequence. To overcome this problem, we applied a liquid-phase oligonucleotide synthesis strategy and describe for the first time the crystal structure of a trypanosomatid eIF4E (T. cruzi EIF4E5) in complex with cap-4. The TcEIF4E5-cap-4 structure allowed a detailed description of the binding mechanism, revealing the interaction mode for the AACU sequence, with the bases packed in a parallel stacking conformation and involved, together with the methyl groups, in hydrophobic contacts with the protein. This binding mechanism evidences a distinct cap interaction mode in comparison with previously described eIF4E structures and may account for the difference of TcEIF4E5-cap-4 dissociation constant in comparison with other eIF4E homologues.

Antibiotic resistance is a worldwide threat due to the decreasing supply of new antimicrobials. Novel targets and innovative strategies are urgently needed to generate pathbreaking drug compounds. NAD kinase (NADK) is essential for growth in most bacteria as it supports critical metabolic pathways. Here, we report the discovery of a new class of antibacterials that targets bacterial NADK. We generated a series of small synthetic adenine derivatives to screen those harboring promising substituents in order to guide efficient fragment linking. This led to NKI1, a new lead compound inhibiting NADK that showed in vitro bactericidal activity against Staphylococcus aureus. In a murine model of infection, NKI1 restricted survival of the bacteria, including methicillin-resistant S. aureus. Collectively, these findings identify bacterial NADK as a potential drug target and NKI1 as a lead compound in the treatment of staphylococcal infections.

2′-Deoxynucleosides of imidazole-4 (or 1,2,4-triazole-3)-carboxamide, ethyl imidazole-4 (or 1,2,4-triazole-3)-carboxylate were synthesized by enzymatic glycosylation using N-deoxyribosyltransferase from a lactobacterium. The base pairing properties of Y and V when placed opposite the natural DNA bases as well as their self were evaluated by thermal denaturation experiments. DNA templates containing imidazole-4-carboxamide base were used in elongation reaction catalysed by Klenow fragment.