In elucidating a novel cell-cycle pathway or mode of regulation, it will first be necessary to establish that the cell is arrested in a particular stage of the cell cycle following arrest-inducing conditions. This is achieved by staining the DNA in a population of cells with propidium iodide and then determining the cell-cycle profile of that population by fluorescence-activated cell sorter (FACS) or by measuring 3 H-thymidine incorporation into DNA as it is being replicated.
