PrLD and IDD are crucial for cytoprotective Hsp42 activity during heat stress. (A) Schematic diagram of the growth competition assay. S. cerevisiae WT cells expressing BFP and indicated hsp42 mutant cells expressing GFP were mixed 1:1. Mixtures were either grown at 30°C or were subjected to heat shock cycles, switching repetitively between 25°C and 43°C. Each day, the proportion of WT and mutant cells was determined by FACS, and cell mixtures were diluted to OD₆₀₀ 0.05. (B) Fractions of Hsp42 WT and Hsp42 deletion mutants or hsp42Δ deletion strain in the mixed cultures upon constant growth at 30°C or repetitive heat stress are plotted. The representative result of one out of three biological replicates is shown.