Radiolabeling of MSP1₁₉, the final processed fragment of MSP1, showing that it remains attached to the parasite after merozoite invasion of erythrocytes, and that it persists within the parasite throughout its life cycle.

<p><i>P. falciparum</i> schizonts were radiolabeled with ³⁵S Met/Cys at 45 hours post-invasion for 1.5 hour and a proportion of these parasites were harvested (S, schizonts). The remaining parasites were allowed to undergo invasion, synchronized (2-hour window) and cultured for the next intraerythrocytic cycle. Parasites were harvested every 6 hours from 0 to 42 hours. Rabbit anti-MSP1-specific antibodies were used to immunoprecipitate labeled protein from NP40-extracts of these parasites. The resulting precipitates were analyzed by SDS-PAGE using a 5–12.5% gradient gel under reducing conditions and visualized by fluorography using X-ray film. The polyclonal anti-MSP1 serum recognized the full-length precursor as indicated by the top arrow in the labeled schizont extract, (S), and the 19-kDa fragment in newly formed ring stages (0 hours), indicated by the bottom arrow. The processed fragment of MSP7, MSP7₃₃ is also detected as part of the MSP1 complex in schizonts (middle arrow). The remaining lanes represent parasites harvested every 6 hours from 6 to 42 hours post-invasion. The intensity and the mobility of the MSP1₁₉ band remained constant until 42 hours when there was some decrease in intensity; this reduction in intensity could be due to rupture of some mature forms releasing MSP1₁₉ into the culture medium. The mobility of protein size markers is indicated at the right of the panel according to their size (kDa).