Src family of tyrosine kinases phosphorylate KIT on Y900 located in the second part of the tyrosine kinase domain. This phosphorylated tyrosine acts as a docking site for p85alpha regulatory subunit of PI3K and the adapter protein CRKII. CRKII does not interact directly with KIT but is recruited indirectly by binding to p85alpha subunit of PI3K. Thus, in this case the p85 subunit acts as an adapter between KIT and CRKII, and not to recruit PI3-kinase. (Lennartsson et al. 2003).