IgG, rabbit muscle aldolase, and BSA were taken from gel
filtration standard kits (catalog no. 17-0442-01, Amersham
Pharmacia). Hen egg lysozyme (HEL) was purchased from
Worthington, and D1.3 antibody was prepared as described in
ref. 29. A DNA fragment encoding the SH3 domains of phospholipase
C1 (790–851) (PLC1) was cloned in the vector
pGEX-4T-1() (Novagen) and expressed in Escherichia coli
BL21-CodonPlus(DE3)-RIL cells (Stratagene). The GST–
PLC1–SH3 fusion protein was purified by using a GSTrap FF
column (Amersham Pharmacia), digested with thrombin protease
(Amersham Pharmacia), and further purified by gel filtration
and anion exchange chromatography. The proline-rich
region of SH2-domain-containing leukocyte protein 76 (SLP-76)
(158–244) was cloned in the vector pET 28a and expressed in E.
coli BL21 cells. His-tagged SLP-76 protein was purified from a
soluble fraction with a HisTrap HP column (Amersham Pharmacia)
followed by gel filtration and anion exchange chromatography.