FIG. 7.

Mammalian HSF1 as well as chicken HSF1 is a survival factor in DT40 cells. (A) Double-null cells were stably transfected with an expression vector for cHSF1, hHSF1, or cHSF3. Protein levels of HSF1, HSF3, and Hsp90 were determined by Western blot analysis in wild-type cells (wt), HSF1-null cells (line 47), HSF3-null cells (line 21), double null cells (line 54), and null cells reexpressing cHSF1(E7), hHSF1 (G7), or cHSF3 (F31). (B) Proportions of sub-G₁ fractions in the cells described in A are shown before (open bar) and after (hatched bar) incubation at 43.5°C for 24 h. All of the double-null cells died after the treatment. Note that the reexpression of hHSF1 completely restored cell survival after heat treatment.