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This Week in Science: Feb 23, 2018

In Science this week, an international research team presents a genomic study suggesting that the oldest known domesticated horse population — which came from the Eneolithic Botai culture of the Central Asian steppes roughly 5,500 years ago — did not give rise to modern-day domesticated horses. By analyzing the genomes of 88 ancient and modern horses — including 20 from the Botai region — they found that all domestic horses from around 4,000 years ago to present only show just 2.7 percent of Botai-related ancestry. "This indicates that a massive genomic turnover underpins the expansion of the horse stock that gave rise to modern domesticates, which coincides with large-scale human population expansions during the Early Bronze Age," they write. GenomeWeb has more on this study, here.

Also in Science, a Delft University of Technology-led team describes how it visualized, for the first time, structural maintenance of chromosome (SMC) protein complexes spatially organizing chromosomes by extruding DNA into large loops. By tethering both ends of a double-stranded piece of DNA to a surface and staining it, they could track it as the complexes worked along the strand. They found that a single condensin complex is able to extrude tens of kilobase pairs of DNA at a force-dependent speed of up to 1,500 base pairs per second, using the energy of ATP hydrolysis. Notably, the DNA loop extrusion process is asymmetric, which demonstrates that condensin anchors onto DNA and reels it in from only one side, the authors write. "Active DNA loop extrusion by SMC complexes may provide the universal unifying principle for genome organization," they add.