Protein tyrosine phosphatases (PTPs) are known to be signaling molecules that regulate a variety of cellular processes, including cell growth, differentiation, mitotic cycle, and oncogenic transformation. PTP receptor type J possesses an extracellular region containing five fibronectin type III repeats, the transmembrane region included in this Pfam entry, and a intracytoplasmic catalytic domain. This entry probably contains part of a Fn3 domain at the N-terminus.