Fig. 7. Uptake of fluorescent yeast particles by VatMpr () and AX3 ([UNK]) cells. Cells were cultured on a suspension of K. aerogenes for 2 days prior to the assay. Bacteria were washed away and the cells were swirled on a rotary shaker for 30-40 minutes before TRITC-yeast particles were added (see Materials and Methods for details). At T₀ and 20 minute intervals thereafter, duplicate samples were taken, the fluorescence of uningested yeast particles was quenched and the fluorescence of the internalized particles was determined. Uptake was linear throughout the 2 hour assay for mutant cells and during the first 80 minutes for wild-type cells. At longer times wild-type values reached a steady state that presumably reflected complete transit of particles through the endo/lysosomal pathway and exocytosis of the undigested remnants. Comparison of linear regression plots for the first 80 minutes showed that the rate of particle uptake by wild-type cells was twice that of VatMpr cells.