FIG. 4.

Cell viability after heat shock is enhanced by hsc70 and hsp70, and this requires the chaperone function of hsp70. Noninduced (OFF) and induced (ON) cells were heated at 43°C for 60 min and returned to 37°C for 24 h. Flow-cytometric cell counts were carried out before the heat shock and after the 24-h recovery period. Separate cultures of nonheated cells were also counted at the same times. Cell numbers at the end of the recovery period are plotted relative to the initial cell count for control (open bars) and heated cells (solid bars). Shown are the means plus the standard errors for three independent experiments. Only the cells expressing hsc70 or hsp70 have significantly higher numbers of viable cells after heat shock (*, P values of a one-tailed t test comparing the relative cell numbers after heat shock for the ON and OFF cells are 0.033 for the HSC70 cell line and 0.022 for the HSP70 cell line; all other P values are greater than 0.1).