CDK1 and infection: In HPV11 and HPV31, the E1 protein, a DNA helicase/ATPase involved in initiating viral DNA replication, shuttles from the cytoplasm into the nucleus after phosphorylation by ERK and/or JNK, and remains in the nucleus because of the presence of activated CDK1/2, which can phosphorylate a CRM-1 dependent NES which inhibits E1 nuclear export, allowing an enhancement of viral DNA replication with appropriate timing during productive infection (reviewed in [55]).