Figure 7.

Kinase activity toward Ser-287 of Xenopus Cdc25 in egg extracts lacking Xcds1 and/or Xchk1. (A) M-phase extracts were immunodepleted with anti-Xcds1 antibodies, anti-Xchk1 antibodies, both anti-Xcds1 and anti-Xchk1 antibodies, or nonspecific rabbit IgG. The treated extracts were activated with CaCl₂ and incubated at 23°C for 90 min in the presence or absence of poly(dT)₄₀. Finally, total kinase activity toward GST-Cdc25[254–316]-WT (WT) or GST-Cdc25[254–316]-S287A (MU) was assayed in each sample. (B) Quantitation of the data shown in A. Only kinase activity toward GST-Cdc25[254–316]-WT was quantitated, because phosphorylation of the S287A mutant was negligible.