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Fig. 2 | Biological Research

Fig. 2

From: The SREBP (Sterol Regulatory Element-Binding Protein) pathway: a regulatory bridge between carotenogenesis and sterol biosynthesis in the carotenogenic yeast Xanthophyllomyces dendrorhous

Fig. 2

The SREBP pathway in A mammals and B X. dendrorhous. The SREBP pathway is involved in the regulation of lipid homeostasis and metabolism, and is regulated by several independent mechanisms including the use of subcellular compartmentalization to ensure its activation, when required. In sterol-replete mammalian cells, the Insig proteins (isoforms: Insig-1 and Insig-2) bind cholesterol-loaded protein SCAP to retain the SCAP-SREBP complex in the endoplasmic reticulum membrane. On the other hand, when cells are depleted of sterols, the SREBP-SCAP complex is transported to the Golgi apparatus where SREBP is sequentially processed by proteases S1P and S2P. As a result, the N-terminal domain (NH2) of SREBP, which contains the basic helix-loop-helix leucine zipper (bHLH-LZ) domain, is released, migrates to the nucleus, and binds as a dimer to the sterol regulatory elements (SREs) in the promoter region of target genes activating their transcription. In X. dendrorhous, the SREBP homolog is Sre1, which is processed by a S2P homolog, named Stp1. Figure adapted from [17]

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