FOX (forkhead box) proteins are a family of transcription factors that play important roles in regulating the expression of genes involved in cell growth, proliferation, differentiation, and longevity. Many FOX proteins are important to embryonic development. FOX proteins also have pioneering transcription activity by being able to bind condensed chromatin during cell differentiation processes. The defining feature of FOX proteins is the forkhead box, a sequence of 80 to 100 amino acids forming a motif that binds to DNA. This forkhead motif is also known as the winged helix, due to the butterfly-like appearance of the loops in the protein structure of the domain. Forkhead proteins are a subgroup of the helix-turn-helix class of proteins. Some FOX genes are downstream targets of the hedgehog signaling pathway, which plays a role in the development of basal cell carcinomas. Members of class O (FOXO- proteins) regulate metabolism, cellular proliferation, stress tolerance and possibly lifespan. The activity of FoxO is controlled by post-translational modifications, including phosphorylation, acetylation and ubiquitination.