LAUSR

Abstract One hundred fifty years ago, Friedrich Miescher discovered DNA when he isolated “Nuclein”—as he named it—from nuclei of human pus cells. Miescher recognized his isolate as a new type of molecule equal in importance to proteins. He realised that it is an acid of large molecular weight and high phosphorus content. Subsequently, he discovered Nuclein also in the nuclei of other cell types, realised that it chemically defines the nucleus, and speculated on its role in proliferation, heredity and fertilisation. While now universally recognised as the discoverer of DNA, whether Miescher also discovered RNA has not yet been addressed. To determine whether his isolation also yielded RNA, we first reproduced his historic protocols. Our resulting modern Nuclein contained a significant percentage of RNA. Encouraged by this result, we then analysed a sample of Nuclein isolated by Miescher from salmon sperm. Assuming that the RNA present in this sample had degraded to nucleobases, we tested for the presence of uracil in the historic Nuclein. Detection of significant levels of uracil by LC-UV-MS demonstrates that Miescher isolated both forms of nucleic acid—DNA and RNA—and underlines the fundamental nature of his discovery for the field of molecular genetics.