Figure 3.
(A) G1/S and mitotic cdks phosphorylate Cdc18 in vitro. Cig2/Cdc2 and Cdc13/Cdc2 kinases were prepared by immunoprecipitation and equal amounts of kinase (based on histone H1 kinase activity) were used to phosphorylate GST or GSTcdc18. 0, no kinase substrate control. (B) G1/S and mitotic cyclins associate with Cdc18. GST or GSTcdc18 was coexpressed with HA-tagged Cig2 or with HA-tagged Cdc13 in fission yeast, and the GST proteins were purified. Equal amounts of GST and GSTcdc18 were fractionated on SDS/polyacrylamide gels, transferred to nitrocellulose, and probed for GST (anti-GST) and for tagged Cig2 or Cdc13 using the anti-HA mAb 12CA5.