RNAi takes on DNA

RNAi takes on DNA NAi may carry out direct silencing not only of RNAs but also of DNA, according to new results from Tom Volpe, Shiv Grewal, Rob Martienssen, and colleagues (Cold Spring Harbor Laboratory (CSHL), Cold Spring Harbor, NY), and Brenda Reinhart and David Bartel (Whitehead Institute, Cambridge, MA). Another group, led by Kazufumi Mochizuki and Martin Gorovsky (University of Rochester, Rochester, NY), has found that similar machinery may be used to chop out DNA segments in Tetrahymena . Both systems illustrate a solution to a puzzling problem in chromatin biology. How can such a wide variety of sequences be recognized and directed toward a single fate¡ªeither silencing in heterochromatin or processing in Tetrahymena ? RNAi may provide the answer.