Ian Mackay of Virology Down Under fame (or notoriety B-) today alerted me to a new paper on the evolution of viruses – which is being touted via press releases as being something that “…adds to evidence that viruses are alive”.
To my mind at least, it does nothing of the sort: what it does do is provide evidence via the medium of comparison of protein folds that “…implies the existence of ancient cellular lineages common to both cells and viruses before the appearance of the “last universal cellular ancestor” that gave rise to modern cells”.
Arshan Nasir and Gustavo Caetano-Anollés took advantage of the fact that protein structure is at least 3 to 10 times more conserved than sequence, and analysed all of the known folds in 5080 organisms, including 3460 viruses. They identified 442 protein folds shared between cells and viruses, and 66 that are unique to viruses – indicating that virus proteomes truly are more diverse than cellular proteomes.
The press release is rather annoying in places, such as in this excerpt:
“Some giant viruses also have genes for proteins that are essential to translation, the process by which cells read gene sequences to build proteins, Caetano-Anollés said. The lack of translational machinery in viruses was once cited as a justification for classifying them as nonliving, he said.
“This is no more,” Caetano-Anollés said. “Viruses now merit a place in the tree of life. Obviously, there is much more to viruses than we once thought.””
Well, some of us have thought a lot more of viruses for a lot longer, obviously! I have taught for years, for example, that viruses are alive – and just last week this blog has a post on how “The” Tree of Life should in fact be a garden, with a tree and a whole lot of bushes.
I do like this bit from the paper itself, however:
“The most parsimonious hypothesis inferred from proteomic data suggests that viruses originated from multiple ancient cells that harbored segmented RNA genomes and coexisted with the ancestors of modern cells.”
The authors have come up with a REAL Tree of Life, as well – one that includes viruses. Smart folk B-)