This is a family of proteins expressed by the crenarchaeon Pyrobaculum aerophilum. The members are highly variable in length and level of conservation. The presence of numerous frameshifts and internal stop codons in multiple alignments are thought to indicate that most family members are no longer functional [1].

1: Genome sequence of the hyperthermophilic crenarchaeon Pyrobaculum aerophilum. Fitz-Gibbon ST, Ladner H, Kim UJ, Stetter KO, Simon MI, Miller JH; Proc Natl Acad Sci U S A 2002;99:984-989. PMID:11792869