Emerging biological functions of the vaccinia-related kinase (VRK) family.

The vaccinia-related kinases (VRKs) branched off early from the family of casein kinase (CK) I and compose a relatively uncharacterized family of the kinome. The VRKs were discovered due to their close sequence relation to the vaccinia virus B1R serine/threonine kinase. They were first described in phosphorylation of transcription factors that led to the discovery of an autoregulatory mechanism between VRK and the tumor suppressor transcription factor p53. The relevance of VRKs has broadened recently by introduction of its members as essential regulators in cell signaling, nuclear envelope dynamics, chromatin modifications, apoptosis and cellular stress response. Several phosphorylation substrates have been described, as well as the first positive and negative regulators of VRK. We provide an overview of the VRKs across species and discuss the wide diversity of cellular and organismal requirements for this kinase family.