Protein transduction has been widely used to analyze biochemical processes in living cells quantitatively and under non-steady-state conditions. The present study analyzed the effects of cell cycle on the uptake and activity of cell-permeant Cre recombinase proteins. Previous studies had suggested that the efficiency of recombination and/or protein transduction varied among individual cells, even within a clonal population. We report here that cells in the G1 phase of the cell cycle undergo recombination at a lower rate than cells at other phases of the cell cycle, and that this variation results largely from differences in protein uptake, associated with differences in cell size. These results have implications regarding the mechanism of protein transduction and identify a source of heterogeneity that can influence the response of individual cells to cell-permeant proteins.
Copyright 2003 Wiley-Liss, Inc.