Protocol for a single-step method for the simultaneous preparation of DNA, RNA, and protein from cells and tissues. The yield of total RNA depends on the tissue or cell source, but it is generally in the range of 4-7 µg/mg starting tissue or 5-10 µg/106 cells. IMPORTANT: Prepare all reagents used in this protocol with Diethyl pyrocarbonate (DEPC)-treated H2O.