CK1 (Casein kinase I) is characterized by its Ser/Thr protein kinase catalytic activity on phoshorylation of casein in vitro in a cycle AMP-independent manner. Six isoforms and CK1-like kinase have been identified in this family. Sequence analysis shows that all members share a N-terminal conserved kinase catalytic domain and a variable C-terminal sequence. Several potential regulatory mechanisms for CK1s have been described including activation via phosphorylation of PKA, 14-3-3 binding and autoinhibition. CK1s are involved in a variety of cellular processes via phosphorylation of a large range of substrates, for instance, stabilizing AIB1 and increasing Erα transcriptional activity, facilitating CK1α/FADD/CaM complex assembly for proper cell cycle progression, reducing DNA-binding activity of Dnmt1, blocking nuclear export and so on. (1)

Reference
1. Cheong, J.K. and Virshup, D.M. (2011) Casein kinase 1: Complexity in the family. Int J Biochem Cell Biol, 43, 465-469. PMID: 21145983

    TTBKs belong to CK1 group and two genes encoding the kinase have been identified which are known as TTBK1 and TTBK2. TTBKs were first described as microtubule-associated proteins (MAPs) which can directly phosphorylate both tubulin and tau at multiple sites. Studies also show that TTBK1 is a neuron-specific kinase that can mediate the phosphorylation of tau and aggreagtion at Alzhieimer's disease related sites. Abnormal expressions of TTBK2 have been reported to contribute ti spinocerebellar ataxia type 11 (1).

Reference
1. Qi, H., Yao, C., Cai, W., Girton, J., Johansen, K.M. and Johansen, J. (2009) Asator, a tau-tubulin kinase homolog in Drosophila localizes to the mitotic spindle. Dev Dyn, 238, 3248-3256. PMID: 19890914

    VRK (vaccinia related kinases) belong to CK1 family. Three members have been identified in human genome, known as VRK1, VRK2 and VRK3. Sequence alignment of VRKs shows that all VRKs share a similar ser/thr protein kinase catalytic domain. Human VRK1 and VRK3 also contain a nuclear localization signal region and VRK2 contain a transmembrane domain in its C-terminal. VRKs act as key activator for activation or stabilization of a variety of transcription factors, including p53, ATF1, c-Jun and CREB. In addition, VRKs play an important role in regulation of cellular processes, including stress response and patterning of chromatin modifications (1).

Reference
1. Klerkx, E.P., Lazo, P.A. and Askjaer, P. (2009) Emerging biological functions of the vaccinia-related kinase (VRK) family. Histol Histopathol, 24, 749-759. PMID: 19337973