NUCLEIC ACIDS
Condensin protein complex pulls DNA into loops Molecular motor helps maintain chromosome structure by extruding DNA loops “For many years, I was very critical of In the new study, the researchers A protein complex known as condensin is this idea that condensin could work as a anchored both ends of a long piece of one of a family of complexes responsible DNA extrusion motor,” Haering says. “But fluorescently labeled double-stranded for organizing and compacting chromonow that we can see it, I think there’s no DNA to a surface. They added fluoressomes so they fit in cells. Condensin’s doubt about it.” cently labeled condensin and adenosine specific job is organizing chromosomes Frank Uhlmann, a researcher at the triphosphate as an energy source and so they can segregate properly during cell Francis Crick Institute who studies mechapplied a constant flow of buffer soludivision. Some researchers have proposed anisms of chromosome segregation, that these complexes work calls the finding exciting. But he by extruding DNA in loops. still has questions. But scientists have nevAnchor “The field has almost comer directly observed this Loop plete knowledge of condenextrusion. Condensin extrusion sin’s molecular structure, but Cees Dekker of Delft the known ATP binding site University of Technology, and the candidate DNA binding Christian H. Haering of the regions don’t add up to a plausiEuropean Molecular Biology Motor ble mechanism for condensin movLaboratory, and coworkers action ing along the DNA,” Uhlmann says. He have now used fluorescence wonders whether condensin really moves microscopy to watch conThe protein complex condensin anchors along the DNA by itself or if it needs andensin make DNA loops (Science 2018, on DNA and acts as a motor to extrude a other enzyme to help it. DOI: 10.1126/science.aar7831). large loop. Camilla Björkegren (formerly Sjögren), Condensin is a ring-shaped complex of who studies chromosome biology at the tion to help stretch out the DNA. five proteins. The mechanism by which Karolinska Institute, finds the work beau“We see a condensin land on the DNA it works has been a subject of debate in tiful, but she too has questions. “This is and start to extrude a loop,” Dekker says. chromosome biology for decades. One naked DNA. What will it look like in the Simultaneous imaging of both the DNA school of thought suggests that condensin context of chromosomes,” which contain and protein complex demonstrated that just clamps existing DNA loops together. histone proteins and other components a single condensin complex at the base The other camp proposes that condensin of structures called nucleosomes? is actually a molecular motor that extrudes of the loop reels in DNA asymmetricalThose are the kinds of questions that the DNA loops itself. Another question has ly: One side of the ring holds on to the Dekker and Haering plan to focus on strand while the other pulls the DNA been how many complexes are involved— next.—CELIA ARNAUD through. just one or more than one?
METAL-ORGANIC FRAMEWORKS
C R E D I T: S CI E NC E
Introducing our new podcast, Stereo Chemistry Metal-organic frameworks are so hot right now, and we wanted to know why. In our first full episode of Stereo Chemistry, we talk to Omar Yaghi, who recently earned a share of the Wolf Prize in Chemistry for his MOF work (see page 43); Omar Farha, who helped build a company around MOFs; and other chemists not named Omar to better understand these materials. Listen to the episode at cenm.ag/moftalk. Subscribe to Stereo Chemistry now on iTunes, Google Play, or TuneIn.—MATT DAVENPORT MARCH 5, 2018 | CEN.ACS.ORG | C&EN
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