The STAT1 gene is a member of the STAT protein family and encodes 2 isoforms of STAT1, α and β. They undergo phosphorylation in response to cytokines and growth factors by the receptor associated kinases, and then form homo- or heterodimers that translocate to the cell nucleus where they act as transcription activators. This protein function as signal transducer and transcription activator that mediates cellular responses to interferons (IFNs), cytokine KITLG/SCF and other cytokines and other growth factors. It also mediates the expression of a variety of genes, which is thought to be important for cell viability in response to different cell stimuli and pathogens. Defects in this protein are the cause of immunodeficiency 31B (IMD31B), immunodeficiency 31A (IMD31A), and immunodeficiency 31C (IMD31C), disorders characterized by susceptibility to severe mycobacterial and viral infections.