Figure 1.

Ydj1p specifically activates the ATPase activity of Ssa1p. (A) Ssa1p (filled circles) or BiP (open circles) was incubated with increasing amounts of Ydj1p for 1 h at 30°C. ATP hydrolysis was assessed by determining the fraction of [α-³²P]ATP converted to [α-³²P]ADP as described in MATERIALS AND METHODS. Data represent the means of at least six independent assays. The mean specific activities (nanomoles of ATP hydrolyzed per minute per milligram of hsc70) of Ssa1p and BiP in these experiments were 1.38 and 1.22 nmol·min⁻¹·mg⁻¹, respectively. (B) Ssa1p or BiP was incubated with or without GST–63Jp for 1 h at 30°C, and ATP hydrolysis was assessed as described above. Data represent the means of at least four independent assays (± SD). The mean specific activities (nmoles of ATP hydrolyzed per minute per milligram of hsc70) of Ssa1p and BiP in these experiments were 1.1 and 0.36 nmol·min⁻¹·mg⁻¹, respectively.