Precursor of the transcription factor form (Processed sterol regulatory element-binding protein 2), 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 (PubMed:32322062). Key transcription factor that regulates expression of genes involved in cholesterol biosynthesis (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:7903453, PubMed:12177166). Regulates transcription of genes related to cholesterol synthesis pathway (PubMed:12177166, PubMed:32322062). Forms a tight complex with SCAP, the SCAP-SREBP complex, in the endoplasmic reticulum membrane (PubMed:19706601, PubMed:32322062). Interacts (via C-terminal domain) with RNF139 (PubMed:19706601). Homodimer; efficient DNA binding of the soluble transcription factor fragment requires dimerization with another bHLH protein (By similarity). Interacts with LMNA (By similarity). At high sterol concentrations, the SCAP-SREBP is retained in the endoplasmic reticulum (PubMed:32322062). Low sterol concentrations promote recruitment into COPII-coated vesicles and transport of the SCAP-SREBP to the Golgi, where it is processed (PubMed:32322062). Transported into the nucleus with the help of importin-beta. Dimerization of the bHLH domain is a prerequisite for importin beta-dependent nuclear import. Ubiquitously expressed in adult and fetal tissues. Processed in the Golgi apparatus, releasing the protein from the membrane (PubMed:8626610, PubMed:32322062, PubMed:9651382, PubMed:10805775). At low cholesterol the SCAP-SREBP complex is recruited into COPII vesicles for export from the endoplasmic reticulum (PubMed:8626610, PubMed:32322062, PubMed:9651382, PubMed:10805775). In the Golgi, complex SREBPs are cleaved sequentially by site-1 (MBTPS1, S1P) and site-2 (MBTPS2, S2P) protease (PubMed:8626610, PubMed:9651382, PubMed:10805775, 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:9651382, PubMed:10805775). Apoptosis triggers cleavage by the cysteine proteases caspase-3 and caspase-7. Cleavage and activation is induced by mediated cholesterol efflux (PubMed:8643593). Phosphorylated by AMPK, leading to suppress protein processing and nuclear translocation, and repress target gene expression. Ubiquitinated; the nuclear form has a rapid turnover and is rapidly ubiquitinated and degraded by the proteasome in the nucleus. Belongs to the SREBP family. Extended N-terminus.