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This Week in Cell: Apr 5, 2017

Researchers from Israel, the US, and the UK explore the evolutionary events that may reintroduce virulence to the attenuated polio virus strain used in vaccines. The team did a phylogenetic analysis focused on more than 400 circulating vaccine-derived polioviruses, folding in theoretical analyses and findings from new genome sequencing on attenuated oral polio vaccine type 2 viruses that were shed a couple weeks after vaccination in 11 vaccinated individuals. In most of the virulent, vaccine-derived isolates, the group identified recombinant events affecting a limited number of genome regions — results supported by subsequent cell line and mouse model experiments.  

A team based at Boston University and Massachusetts Institute of Technology considers the possibility that an ancient, phosphate-free form of metabolism preceded the phosphate-dependent metabolic methods employed by living organisms today. By computationally constructing metabolic networks that contained compounds that would have existed prebiotically but did not contain phosphate-dependent reactions, the researchers found evidence that a network rich in iron-sulfur-using enzymes could have produced "a broad category of key biomolecules."  The authors note that "[o]ur results corroborate and expand previous proposals that a putative thioester-based metabolism could have predated the incorporation of phosphate and an RNA-based genetic system."

Swiss researchers report on regulatory RNAs formed through "concatenation and circularization of excised DNA segments." Using the Paramecium tetraurelia model organism, the team did a series of genomics-informed experiments and small RNA sequencing analyses to look at mechanisms by which Piwi-associated small RNAs become formed from very short, transposon-derived DNA sequences called internal eliminated sequences. "The generation of [internal eliminated sequence RNAs] has been a mystery due to the very short length of the supposed template," the study's authors say. "Here, we demonstrate that Paramecium has evolved a previously undescribed mechanism for transcribing short DNA pieces — their concatenation and circularization."