description Blastocystis sp. is a highly prevalent anaerobic eukaryotic parasite of humans and animals. The genome of several representatives has been sequenced revealing specific traits such as an intriguing 3’-end processing of primary transcripts. We have acquired a first high-throughput proteomics dataset on the difficult to cultivate ST4 isolate WR1 and detected 2,761 proteins. We evidenced for the first time by proteogenomics a functional termination codon derived from transcript polyadenylation for seven different key cellular components.