In 2005, Suskiewicz et al. classified the enzyme YwIE as a tyrosine phosphatase. And Kirstein et al. (2005) found that McsB is a tyrosine kinase that needs McsA to become activated. They also found that the interaction of McsA and McsB with CtsR results in the formation of a 3-protein complex that stops the binding of CtsR to its target DNA and leads to subsequent phosphorylation of McsB, McsA, and CtsR.