We examined whether the fast release of replicon initiation after sudden O2 recovery of hypoxically incubated mammalian cells depends on kinase activity of Cdk2. We used a system based on starved⁄refed T24 cells elab-orated previously for such investigations [van Betteraey-Nikoleit M, Eisele KH, Stabenow D & Probst H (2003)Eur J Biochem270, 3880–3890].