This is family of microsporidia-specific sequences with no known function. There is a very characteristic NPW sequence motif at the very C-terminus.

1: Reduction and expansion in microsporidian genome evolution: new insights from comparative genomics. Nakjang S, Williams TA, Heinz E, Watson AK, Foster PG, Sendra KM, Heaps SE, Hirt RP, Martin Embley T; Genome Biol Evol. 2013;5:2285-2303. PMID:24259309