cDNA Isolated from a Human T-Cell Library Encodes a Member of the Protein-Tyrosine-Phosphatase Family

A human peripheral T-cell cDNA library was screened with two labeled synthetic oligonucleotides encoding regions of a human placenta protein-tyrosine-phosphatase (protein-tyrosine-phosphate phosphohydrolase, EC 3.1.3.48). One positive clone was isolated and the nucleotide sequence was determined. It contained 1305 base pairs of open reading frame followed by a TAA stop codon and 978 base pairs of 3′ untranslated end, although a poly(A)+ tail was not found. An initiator methionine residue was predicted at position 61, which would result in a protein of 415 amino acid residues (Mr, 48,400). This was supported by the synthesis of a Mr 48,000 protein in an in vitro reticulocyte lysate translation system using RNA transcribed from the cloned cDNA and T7 RNA polymerase. The deduced amino acid sequence was compared to other known proteins revealing 65% identity to the low Mr PTPase 1B isolated from placenta. In view of the high degree of similarity, the T-cell cDNA likely encodes a newly discovered protein-tyrosine-phosphatase, thus expanding this family of genes.