Figure 2. CD loop elongation in the SH2 domain results in reduced kinase activity of full length Csk towards its physiological substrate Src.

Wild type Csk's (circle) and the variant's (square) kinase activity was monitored in a [γ-³²P]ATP coupled radioactive assay in which a kinase dead substrate (kdSrc) is phosphorylated as a function of time. The reactions typically included 200 nM Csk, 20 µM kdSrc, and 50 µM ATP at 23°C.