Left is right, right is wrong.

correspondence correspondence Left is right, right is wrong T he cover illustration of the August 2009 issue of EMBO reports, although aesthetically pleasing, is unfortunately erroneous and could come as a shock to researchers in the chromatin field. Canonical nucleosomes are indeed left-handed, such as the nucleosomes in the left 'column' of chro-matin fibres on the cover. However, in the right 'column', the chirality of the nucleo-somes has been inverted: they are drawn in a non-canonical, right-handed conformation. This mistake is sadly quite common: many textbooks, publications and websites feature images of nucleosomes displaying the wrong chirality. Try a search for " nucle-osome " in Google Images: there is a good chance that the first hit will display the right-handed nucleosome originally—and incorrectly—drawn for a popular textbook. To make things worse, this image has been frequently adapted in many other contexts. For instance, it acts as an illustration for the Wikipedia nucleosome entry in several languages, including French. If you would like more examples, I am happy to provide a full collection of 'wrong' nucleosomes on request. Nucleosomes depicted with right-handed chirality are usually the result of inadvertent infographics errors, because many artists who draw chromatin fibres are perhaps not aware of chirality matters. They also arise if the image of a canonical nucleo-some is accidentally mirrored upon publication (Fig 1A,B). This was the case in another popular textbook, in which the mirror image managed to survive several editions—and the scrutiny of thousands of teachers and students—before I finally mentioned it to the authors, who promptly fixed it in the following edition. Note also that if the DNA helix is resolved on these erroneous images, mirror inversion will also inverse its canoni-cal right-handedness (Fig 1B). DNA is another victim of neglected chirality, which results in journal covers, advertisements and other pictures ending up full of left-handed DNA that is not intended to be Z-DNA. I would therefore encourage readers to play the 'chirality game': each time you see a nucleo some or a DNA molecule, check its handedness! Incidentally, while this text was being edited, another journal provided an appropriate entry for the chirality game: on the cover of Nature Structural and Molecular Biology's September issue, the first nucleosome is left-handed, whereas the second is right-handed. Who will be next? Should we care so much about nucleo-some chirality? The answer is yes, because nucleosome chirality must have evolved as a …