Fos protein is a type of protein that plays a crucial role in cellular processes, particularly in regulating gene expression. It is part of a larger family of proteins known as AP-1, which are involved in controlling various biological functions, including cell growth, differentiation, and response to stress. Fos proteins are often activated in response to external signals, such as growth factors or stressors. These proteins work by forming complexes with other proteins, such as Jun, to bind to specific DNA sequences and influence the transcription of target genes. This regulation is essential for processes like development, immune response, and the healing of injuries. Understanding Fos protein and its functions can provide insights into various diseases, including cancer.