Precursor of the transcription factor form (Processed sterol regulatory element-binding protein 1), which is embedded in the endoplasmic reticulum membrane (PubMed:32322062). Low sterol concentrations promote processing of this form, releasing the transcription factor form that translocates into the nucleus and activates transcription of genes involved in cholesterol biosynthesis and lipid homeostasis (By similarity). Key transcription factor that regulates expression of genes involved in cholesterol biosynthesis and lipid homeostasis (PubMed:8402897, PubMed:12177166, PubMed:32322062). Binds to the sterol regulatory element 1 (SRE-1) (5'-ATCACCCCAC-3'). Has dual sequence specificity binding to both an E-box motif (5'-ATCACGTGA-3') and to SRE-1 (5'-ATCACCCCAC-3') (PubMed:8402897, PubMed:12177166). Regulates the promoters of genes involved in cholesterol biosynthesis and the LDL receptor (LDLR) pathway of sterol regulation (PubMed:8402897, PubMed:12177166, PubMed:32322062). Isoform expressed only in select tissues, which has higher transcriptional activity compared to SREBP-1C (By similarity). Able to stimulate both lipogenic and cholesterogenic gene expression (PubMed:12177166, PubMed:32497488). Has a role in the nutritional regulation of fatty acids and triglycerides in lipogenic organs such as the liver (By similarity). Required for innate immune response in macrophages by regulating lipid metabolism (By similarity). Predominant isoform expressed in most tissues, which has weaker transcriptional activity compared to isoform SREBP-1A (By similarity). Primarily controls expression of lipogenic gene (PubMed:12177166). Strongly activates global lipid synthesis in rapidly growing cells (By similarity). The absence of Golgi proteolytic processing requirement makes this isoform constitutively active in transactivation of lipogenic gene promoters. The absence of Golgi proteolytic processing requirement makes this isoform constitutively active in transactivation of lipogenic gene promoters. Forms a tight complex with SCAP, the SCAP-SREBP complex, in the endoplasmic reticulum membrane. Efficient DNA binding of the soluble transcription factor fragment requires dimerization with another bHLH protein (PubMed:8402897). Interacts with CEBPA, the interaction produces a transcriptional synergy (By similarity). Interacts with LMNA (By similarity). At high sterol concentrations, the SCAP-SREBP is retained in the endoplasmic reticulum. Low sterol concentrations promote recruitment into COPII-coated vesicles and transport of the SCAP-SREBP to the Golgi, where it is processed. Additional isoforms seem to exist. Expressed in a wide variety of tissues, most abundant in liver and adrenal gland (PubMed:8402897). In fetal tissues lung and liver shows highest expression (PubMed:8402897). Predominates in hepatoma cell lines (PubMed:8402897). Also expressed in kidney, brain, white fat, and muscle (PubMed:8402897). Predominantly expressed in liver and adipose tissues (PubMed:8402897). Also expressed in kidney, brain, white fat, and muscle (PubMed:8402897). The 9aaTAD motif is a transactivation domain present in a large number of yeast and animal transcription factors. Processed in the Golgi apparatus, releasing the protein from the membrane (PubMed:8626610, PubMed:32322062). At low cholesterol the SCAP-SREBP complex is recruited into COPII vesicles for export from the endoplasmic reticulum (PubMed:8626610, PubMed:32322062). In the Golgi, complex SREBPs are cleaved sequentially by site-1 (MBTPS1, S1P) and site-2 (MBTPS2, S2P) protease (PubMed:8626610, PubMed:32322062). The first cleavage by site-1 protease occurs within the luminal loop, the second cleavage by site-2 protease occurs within the first transmembrane domain, releasing the transcription factor from the Golgi membrane (PubMed:32322062). Phosphorylated by AMPK, leading to suppress protein processing and nuclear translocation, and repress target gene expression (By similarity). Phosphorylation at Ser-402 by SIK1 represses activity possibly by inhibiting DNA-binding (By similarity). Ubiquitinated; the nuclear form has a rapid turnover and is rapidly ubiquitinated and degraded by the proteasome in the nucleus. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Belongs to the SREBP family. Truncated N-terminus. Intron retention. Sterol regulatory element-binding protein entry