Transcriptomic analysis of genes upregulated in bradyzoite stages and predicted to contain a signal peptide has been used to discover cyst wall proteins and led to the identification of MCP4 and BPK1 (6); however, this strategy also has limitations, as signal peptide prediction and bradyzoite transcript abundance may not predict all of the bradyzoite secreted proteins that localize to the cyst wall. This evidence concerns the gene PROS1 and cyst.