Figure 3. Hog1 is dispensable for regulation of Fps1 gating under hyperosmotic condition.

(a) Schematic diagram of Fps1 regulation. Fps1 gating appears to be regulated by phosphorylation at Thr²³¹ and eviction of its positive regulator Rgc2 (not shown), which are mediated by Hog1 and other kinases. Unregulated Fps1 (N-terminal truncated or Thr²³¹ mutants) cannot close the gate and consequently causes osmosensitivity because of constitutive glycerol leakage. (b) The presence or absence of Fps1 does not affect synthetic osmoadaptation, while expression of Fps1-Δ1 prevents it. Cells of the hog1Δ PFUS1-GPP2 PFUS1-GPD1^4A strains with vector (pRS403), FPS1 deletion, or Fps1-Δ1 (pRS403-FPS1-Δ1) were grown on YPD plates with or without 0.8 M KCl for 1–2 days at 30°C. Cell growth shown in (b) correlates well with the ability of those cells to accumulate glycerol (c) and recover cell volume (d) after osmotic treatment. For cell volume data, line thickness indicates standard deviation of data obtained with approximately 30 cells. See Methods for the details of glycerol assay and cell volume measurement.