RCK
The RCK branch is the smallest limb of the CMGC group, containing only three human kinases: MAK, MOK and ICK, the last also named CILK1. All are CDK relatives distinguished by a long C-terminal extension and by tissue-restricted expression rather than cyclin-driven cell-cycle control. MAK concentrates in photoreceptor outer segments, where it supports microtubule dynamics at the connecting cilium, and mutations that disrupt its regulation cause autosomal recessive retinitis pigmentosa. ICK operates in ciliary compartments, and its loss causes endocrine-cerebro-osteodysplasia syndrome, a lethal ciliopathy. MOK is broadly expressed with physiological roles still undefined. None of the three is activated by canonical cyclin binding.
