CLONING, EXPRESSION AND CHARACTERIZATION OF A NEW HUMAN LOW M-R PHOSPHOTYROSINE PROTEIN PHOSPHATASE ORIGINATING BY ALTERNATIVE SPLICING

RT-PCR experiments on RNA from K562 and HepG2 cells and from human pla centa led to the isolation of a novel cDNA, a further alternative spli cing product of the primary transcript of low Mr phosphotyrosine phosp hatase (LMW-PTP), already known to produce isoforms 1 and 2, This new transcript represents 15-20% of the total LMW-PTP mRNA in the cell. Th is novel cDNA codifies for a protein that me have named SV3 (splicing variant 3): the deduced protein sequence presents the first 49 residue s identical to those of isoform 1, followed by 24 unrelated amino acid s, due to a frameshift introduced at the novel exon-exon boundary. The SV3 protein, expressed in E, coli is enzymatically inactive, most pro bably because unfolded, as suggested by far-UV circular dichroism (CD) experiments, SV3 protein appears to possess the characteristics of an unstructured polypeptide chain lacking the packing of side chain resi dues and the secondary structure level that are typical of globular pr oteins, This protein could represent an inactive variant of the human LMW-PTP, (C) 1998 Federation of European Biochemical Societies.