Plastid import assay. Radiolabeled PhCM1, PhCM2, and PsOE23 were individually incubated with isolated pea chloroplasts. After import, the isolated chloroplasts were treated with thermolysin as depicted in the figure. Proteolysis was terminated and the intact chloroplasts were then repurified, washed, lysed, and fractionated. PsOE23 is a thylakoid lumen protein with a stromal intermediate, which was used as a positive control. The translation products (tp), chloroplasts (Cp), thermolysin treated chloroplasts (Cp*), stromal extracts (SE), and total membranes (M) were analyzed with SDS-PAGE and fluorography. Positions of the molecular weight marker are depicted on the left.