Transcription factor that regulates gene expression during development. May play a role in regulating gene expression in response to osmotic stress. Monomer, in the absence of tyrosine phosphorylation. Homodimer, or heterodimer with another family member, when tyrosine phosphorylated. Tyrosine phosphorylation is not required for translocation to the nucleus. DIF inhibits export from the nucleus. Predominantly nuclear in pstO cells at the rear of the prestalk region in the slug. Subject to crm1-dependent nuclear export. Constitutively expressed during development (at protein level). Up-regulated in response to hyperosmotic shock. Tyrosine phosphorylated in response to the chlorinated hexaphenone DIF. Minimally phosphorylated in the absence of DIF. Phosphorylation increases during development, is highest during the slug stage, with a strong decrease at culmination. Cells display abnormal regulation of gene expression and aberrant timing of development. Colonies growing on a bacterial lawn are smaller, have a rough edge and are surrounded by satellite fruiting bodies. Belongs to the transcription factor STAT family.