Figure 1

Vpr induces cell cycle G2/M arrest through activation of Chk1 via Ser³⁴⁵phosphorylation in S phase of the cell cycle. A. HeLa cells synchronized at the G1/S boundary by double thymine (DT) block were transduced with Adv control or Adv-Vpr (MOI 1.0) and released from the block at time 0. The cell cycle profiles measured by DNA content (a) were detected from time 0 to 11 hours after the DT release. The Cdk1-Tyr³⁴⁵ or Chk1-Ser³⁴⁵ phosphorylation status (b) were detected in the Vpr-positive or Vpr-negative cells collected at indicated time. B. HeLa cells, which were first synchronized in M phase by Nocodazole (100 ng/ml), were transduced with Adv or Adv-Vpr and detected the same way as shown in (A). Note that very weak Vpr was detected in (A-b) because Ad-Vpr was only transduced within 5 to 11 hours. The Vpr protein was clearly detected subsequently at about 15 hours after viral transduction (B-b).