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 SREBF1gene.
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 -1c (ADD-1).
The proteins encoded by this gene are transcription factors that bind to a sequence in the promoter of different genes, called sterol regulatory element-1 (SRE1). This element is a decamer flanking the LDL receptor gene and other genes involved in, for instance, sterol biosynthesis. The protein is synthesized as a precursor that is attached to the nuclear membrane and endoplasmic reticulum. Following cleavage, the mature protein translocates to the nucleus and activates transcription by binding to the SRE1. Sterols inhibit the cleavage of the precursor, and the mature nuclear form is rapidly catabolized, thereby reducing transcription. The protein is a member of the basic helix-loop-helix-leucine zipper (bHLH-Zip) transcription factor family.
SREBP-1c regulates genes required for glucose metabolism and fatty acid and lipid production and its expression is regulated by insulin. SREBP-1a regulates genes related to lipid and cholesterol production and its activity is regulated by sterol levels in the cell.
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