RNA extraction by the guanidine thiocyanate procedure

This method relies on the strong chaotropic nature of the reagents involved to completely denature any ribonuclease (RNase) present in the sample. After lysis in guanidine thiocyanate buffers there are two possibilities for isolation of the RNA. One method involves a series of differential precipitation steps in guanidine hydrochloride (1). The alternative, detailed here, involves centrifugation of the samples on a cushion of 5.7M CsCl (2,3). The RNA passes through this cushion, whereas the DNA and the majority of other cellular macromolecules remain above the cushion.