A widespread pathway for substitution of adenine by diaminopurine in phage genomes

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


DNA modifications vary in form and function but generally do not alter Watson-Crick base pairing. Diaminopurine (Z) is an exception because it completely replaces adenine and forms three hydrogen bonds with thymine in cyanophage S-2L genomic DNA. However, the biosynthesis, prevalence, and importance of Z genomes remain unexplored. Here, we report a multienzyme system that supports Z-genome synthesis. We identified dozens of globally widespread phages harboring such enzymes, and we further verified the Z genome in one of these phages, Acinetobacter phage SH-Ab 15497, by using liquid chromatography with ultraviolet and mass spectrometry. The Z genome endows phages with evolutionary advantages for evading the attack of host restriction enzymes, and the characterization of its biosynthetic pathway enables Z-DNA production on a large scale for a diverse range of applications.

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