Anges in the phosphorylation state of proteins lead to specific cellular responses (Cohen, 2000; Moorhead et al., 2009; Pidoux and Tasken, 2009). Eukaryotic kinases themselves often require activation by phosphorylation (Nolen et al., 2004) and are distinguished by their target residue specificities, which for the purposes of this review are either serine/threonine or tyrosine residues (Olsen et a