Mutational analysis of Sse1p function. (A) Schematic representation of a set of Sse1p constructs assayed for their ability to accelerate nucleotide exchange on Ssa1p and Ssb1p. (B, C) Nucleotide exchange activity of the Sse1p constructs on Ssa1p and Ssb1p, respectively. Sse1p variants and Ssa1p or Ssb1p were mixed at a molar ratio of 5:1. In the bar graphs, the average nucleotide exchange activity of wt Sse1p was set to 1. The ATP binding mutant G233D retained only about 5% of wt activity, that is, koff is slightly above the spontaneous release rate.