CDC-like kinase 2 (CLK2) belongs to a family of autophosphorylating kinases termed CLK (CDC2/CDC28-like kinases), which have been shown to phosphorylate serine- and arginine-rich (SR) proteins of the spliceosomal complex, and to influence alternative splicing in overexpression systems. Recent findings demonstrated that the CLK kinases activate PTP-1B family members, and this phosphatase may be an important cellular target for CLK action. Mutations in the CLK2 proteins affect organismal features such as development, behavior, reproduction, and aging as well as cellular features such as the cell cycle, apoptosis, the DNA replication checkpoint, and telomere length.