pp135 associates with the SH3 domains of different proteins. The lysates from UT-7 cells stimulated with GM-CSF (lanes 2, 4, 6, 8, 10, 12, 14, 16, and 18) or unstimulated (lanes 1, 3, 5, 7, 9, 11, 13, 15, and 17) were mixed with each GST-SH3 fusion protein noncovalently coupled to glutathione-agarose beads. The resulting precipitates were subjected to SDS-PAGE and immunoblotted with anti-P6. The arrow indicates the position of pp135.