In this week's Nature Genetics, researchers from the University of California, San Francisco, report data showing that competition between animal mitochondrial genomes is directed by the selfish drive of a genome rather than the functionality it imparts to an organism. To explore how mitochondrial genomes compete for transmission from mother to progeny, the researchers introduced additional genomes into Drosophila. While competitions between closely related genomes favored those functional in electron transport — resulting in host-beneficial purifying selection — competition between distantly related genomes often favored those with negligible, negative, or lethal consequences, indicating selfish selection. In maternal lineages, constant competition among sibling genomes selects for "super-replicators," the authors write, and this competition drives positive selection to promote change in the sequences influencing transmission.
And in Nature Structural & Molecular Biology, a University of Sheffield-led team describes the direct observation of DNA threading in complexes of flap endonucleases — enzymes that trim branched nucleic acids to produce double-helical DNA. They report the crystal structures of bacteriophage T5 flap endonuclease in complexes with intact DNA substrates and products, and described an "unusual" mechanism, dubbed "fly-casting, thread, bend, and barb," behind substrate recognition.