Localization of phosphotyrosine in KG1a cells after stimulation. KG1a cells were stimulated for 30 minutes with anti-CD34 (4A1), anti-CD43 (MEM59), or MOPC21 (control) as described in the legend to Fig 1. After fixation and permeabilization, cells were double-stained with anti-pTyr (green channel: b, f, and j) and phalloidin (red channel: c, g, and k), and analyzed by Nomarski differential-interference-contrast (left-hand panels) and confocal immunofluorescence microscopy. The right-hand panels show superimposed images of green and red channels. Bars, 5 μm.