Figure 2.

Proline residues are required to activate Lck and Fyn. (A) Sequences of mutated CD2 and CD28 peptides used are depicted using the one-letter amino acid code. The mutated residues are shown in bold. (B) Activation of Lck kinase activity by CD28 peptide requires proline residues. Kinase reactions were performed as described in Fig. 1 using wild-type and mutated CD28 peptides. (C) Activation of Fyn kinase activity by CD2 peptide requires proline residues. Kinase reactions were performed as described in Fig. 1 using wild-type and mutated CD2 peptides. All data are representative of at least three independent trials.