• Some Viruses Have a Completely Different Genome to The Rest of Life on Earth

    “Genomic DNA is composed of four standard nucleotides … These nucleobases form the genetic alphabet, ATCG, which is conserved across all domains of life,” biologists Michael Grome and Farren Isaacs write in a recent Science editorial accompanying the new research on bacteriophage genetics.

    “However, in 1977, the DNA virus cyanophage S-2L was discovered with all instances of ’A’ substituted with 2-aminoadenine (Z) throughout its genome forming the genetic alphabet ZTCG.”

    The reason appeared to be self-protection. Within the connecting ’rungs’ of a DNA double helix, the ’Z’ base forms a triple bond to the opposite ’T’ base, one more than the two bonds of the regular A:T connection. This makes the viral genome hardier and more difficult for bacteria to prise apart with chemicals called nucleases.

    Although scientists were fascinated, no other bacteriophages were found with the Z-genome, and with the difficulty of culturing S-2L in a lab, the Z-genome was set aside as a curiosity.

    Now, research documented in three separate studies from researchers in France and China shows that this was not a one-off, whilst also characterizing how the Z-genome works and how it’s assembled.