This domain family is found in eukaryotes, and is approximately 30 amino acids in length. The family is found in association with pfam00041. There is a single completely conserved residue L that may be functionally important. This family consists of various protein tyrosine phosphatase haematopoietic receptors, e.g. CD45, which dephosphorylate growth stimulating proteins. This limits growth signalling in haematopoietic cells.