Prions—infectious protein particles thought to cause “mad cow disease,” human Creutzfeldt-Jakob disease, and other neurological afflictions—now seem to be running rampant in yeast. But there's no reason to stop eating bread or drinking beer, for there's not even a hint that yeast prions pose a health threat. On the contrary, they may help scientists figure out how a protein can perpetuate a trait—or a disease—from one cell to the next without involving DNA or RNA. On page 622, researchers show that a form-changing protein in yeast appears to create a trait called [PSI+] in daughter yeast cells, after they bud off a mother cell, by causing newly synthesized proteins to become relatively insoluble and clump together. It does so without altering the DNA in the cells, which are clones.