Kinetochores are huge. The simplest ones contain more than 250 proteins. This makes sense, considering the kinetochore’s hefty responsibility—connecting chromosomes to the long, thin microtubules that tug them to one end of a dividing cell. Its work is essential to ensuring new cells receive the appropriate allotment of chromosomes.
Janelia Farm Research Campus group leader Tamir Gonen recently published the first-ever three-dimensional image of this huge complex. His colleagues in the Biggins laboratory devised a way to isolate the immense structures from yeast and then worked closely with Gonen’s team to use electron microscopy to see how kinetochores grabbed on to microtubules. The images, published September 2012 in Nature Structural and Molecular Biology, showed that the kinetochore is shaped like the palm of a hand. A large domain in the center could be used to grab the chromosome, the researchers say, while the spokes that radiate out from that center attach to the microtubule.
|A three-dimensional tomographic reconstruction showing a kinetochore complex (pink) bound to a microtubule (yellow).|
“These are very early days for this structure,” Gonen says, noting that the large size and dynamic nature of the kinetochore pose a challenge as structural biologists work toward a higher-resolution picture of the complex. “But with this unprecedented look, people can now begin to explain some of the biochemical data about how kinetochores control chromosome segregation.”