Evolution: bacteriophages weird genome (Evolution)

by David Turell @, Friday, April 30, 2021, 20:05 (13 days ago) @ David Turell

They have a 'z' code:


"Alien’ genomes can be found on Earth. Some viruses that infect bacteria use an alternative genetic alphabet that’s distinct from the code used by nearly all other organisms — and, now, two teams have spelt out how the system works.

"More than four decades in the making, the studies show how dozens of these bacteriophages (or just ‘phages’), as they are known, write their genomes using a chemical base called 2-aminoadenine, Z for short, instead of adenine — the A in the As, Ts, Cs and Gs of genetics textbooks.


"The work is seminal, says Steven Benner, a synthetic biologist and founder of the Foundation for Applied Molecular Evolution in Alachua, Florida, who compares it to US microbiologist Carl Woese’s discovery of a new branch of single-celled life. “It represents the first discovery of a ‘shadow biosphere’ since Woese identified the Archaea a half century ago.”

"Scientists in the Soviet Union were the first to discover Z-DNA, in the late 1970s, in a phage called S-2L, which infects photosynthetic bacteria4. They found that the phage DNA behaved oddly when its two helical strands were melted apart. The bond that forms between G and C bases breaks at a higher temperature, compared with that joining A and T, and the phage’s DNA behaved as if it was made primarily from G and C. But further analysis by the Soviet team showed that the phage had replaced A with Z, which formed a stronger bond with T.


"In 2019, Zhao’s team found similar database matches. Both teams showed that the phages all had a gene named PurZ. This codes for an enzyme that plays an early but crucial part in making the Z nucleotide from a precursor molecule that is present in bacterial cells. They then identified additional enzymes — encoded in the genomes of bacteria that the phages infect — that complete the pathway."

Comment: The article explains that this discovery is only partially understood, but no question of a major difference from all other genomes. A God-created different code from the standard.

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