Edited by Ivan Sadowski Keywords:Signal transducer and activator of transcription 3 STAT3 PEMSA M67 SH2 X-ray crystallography a b s t r a c tThe STAT3 transcription factor plays a central role in a wide range of cancer types where it is overexpressed. Previously, phosphorylation of this protein was thought to be a prerequisite for direct binding to DNA. However, we have now shown complete binding of a purified unphosphorylated STAT3 (uSTAT3) core directly to M67 DNA, the high affinity STAT3 target DNA sequence, by a protein electrophoretic mobility shift assay (PEMSA). Binding to M67 DNA was inhibited by addition of increasing concentrations of a phosphotyrosyl peptide. X-ray crystallography demonstrates one mode of binding that is similar to that known for the STAT3 core phosphorylated at Y705. Structured summary of protein interactions: pSTAT3btc and pSTAT3btc bind by molecular sieving (View interaction)

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