Files in this Data Supplement:

• Supplemental file 1 - Fig. S1 (The Cdk8-β-Geo fusion protein is kinase dead)
  Zipped PDF document, 61K.
• Supplemental file 2 - Fig. S2 (Cdk8^-/- embryos in vitro are affected already at the zygote stage)
  Zipped PDF document, 3.5MB.
• Supplemental file 3 - Legends to Fig. S1 and S2 and supplemental text
  Zipped PDF document, 90K.