The cells were collected by centrifugation, washed twice with 1 ml of phosphate-buffered saline (PBS) and then the pellet was frozen at ±80°C until use. The pellet was resuspended in 0.1 ml of PBS. An aliquot of the suspension was mixed with an equal volume of 8% perchloric acid, vortexed for 1 min, kept on ice for 5 min and centrifuged at 15 000 r.p.m., 4°C for 5 min. Ten microliters of the supernatant were subjected to polyamine analysis using¯uorometry on high-performance liquid chromatography as described previously (Murakami et al., 1989) . Protein concentrations were determined with the BCA protein assay kit (Pierce).