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SH2 regions are protein motifs capable of binding target protein sequences that contain a phosphotyrosine. The solution structure of the abl SH2 product, a protein of 109 residues and 12.1 kd, has been determined by multidimensional nuclear magnetic resonance spectroscopy. It is a compact spherical domain with a pair of three-stranded antiparallel 9 sheets and a C-terminal a helix enclosing the hydrophobic core. Three arginines project from a short N-terminal a helix and one p sheet into the putative phosphotyrosine-binding site, which lies on a face distal from the termini. Comparison with other SH2 sequences supports a common global fold and mode of phosphotyrosine binding for this family.