In Vitro: The hmT-derived phosphopeptide, pY324, which has the sequence EPQpYEEIPIYL, shows the highest affinity binding to GST fusion proteins of the Lck SH2 domain (5-fold higher than Lck’s affinity-for the Lck tail phosphopeptide) and the Src SH2 domain (44-fold higher than Src’s affinity for the Src tail phosphopeptide).