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An archaeal plasmid that can be transported in membrane vesicles, similar to a virus, and encodes proteins that can insert into host membranes and membrane vesicles, provides insights into the evolutionary link between plasmids and viruses.
In the absence of complete genomes, the metabolic capabilities of uncultured ARMAN-like archaea have been uncertain. Here, Golyshina et al. apply an enrichment culture technique and find that the ungapped genome of the ARMAN-like archaeon Mia14 has lost key metabolic pathways, suggesting dependence on the host archaeon Cuniculiplasma divulgatum.
In addition to canonical guide-dependent endonuclease activity, the Argonaute protein from the archaeon Methanocaldococcus jannaschii (MjAgo) is capable of guide-independent DNA cleavage, enabling MjAgo to process plasmids and genomic DNA.
Although not photosynthetic, some archaea possess RuBisCO, one of the enzymes characteristic of the photosynthetic Calvin-Benson cycle, but apparently lack another one, phosphoribulokinase (PRK). Here the authors describe a carbon metabolic pathway in methanogenic archaea, involving RuBisCO and PRK.
How archaeal viruses perturb host transcription machinery is poorly understood. Here, the authors provide evidence that the archaeo-viral transcription factor ORF145/RIP targets host RNA polymerase, repressing its activity.