Sterol regulatory element-binding transcription factor 1 (SREBF1) also known as sterol regulatory element-binding protein 1 (SREBP-1) is a protein that in humans is encoded by the SREBF1 gene. This gene is located within the Smith–Magenis syndrome region on chromosome 17. Two transcript variants encoding different isoforms have been found for this gene. The isoforms are SREBP-1a and SREBP-1c (the latter also called ADD-1). SREBP-1a is expressed in the intestine and spleen, whereas SREBP-1c is mainly expressed in liver, muscle, and fat (among other tissues). SREBP-1 plays a key role in the induction of lipogenesis by the liver. mTORC1 is activated by insulin (a hormone of nutrient abundance) leading to increased production of SREBP-1c, which facilitates storage of fatty acids (excess nutrients) as triglycerides.