FRET between antigen-clustered BCR and Lyn kinase is prolonged and sensitive to PP2 inhibition. (A) Comparison of FRET efficiencies between Igα-YFP and Lyn16-CFP and between Igα-YFP and LynFL-CFP with time. (B) A comparison of the Ea between Igα-YFP and LynFL-CFP in the presence or absence of PP2. The calculation of FRET efficiency was performed as described in Materials and methods. Mean + SEM (error bars) of calculated Ea are shown with time for 12 cells expressing Lyn16-CFP, six cells expressing LynFL-CFP, and three cells expressing LynFL-CFP treated with PP2.