Nuclear import of sterol regulatory element-binding protein-2, a basic helix-loop-helix-leucine zipper (bHLH-Zip) -containing transcription factor, occurs through the direct interaction of importin beta with HLH-Zip
Nagoshi, E.; Imamoto, N.; Sato, R.; Yoneda, Y.
Molecular Biology of the Cell 10(7): 2221-2233
ISSN/ISBN: 1059-1524 PMID: 10397761 DOI: 10.1091/mbc.10.7.2221
The sterol regulatory element-binding protein-2 (SREBP-2) is produced as a large precursor molecule attached to the endoplasmic reticulum membrane. In response to the sterol depletion, the N-terminal segment of the precursor, which contains a basic helix-loop-helix-leucine zipper domain, is released by two sequential cleavages and is translocated to the nucleus, where it activates the transcription of target genes. The data herein show that released SREBP-2 uses a distinct nuclear transport pathway, which is mediated by importin beta. The mature form of SREBP-2 is actively transported into the nucleus when injected into the cell cytoplasm. SREBP-2 binds directly to importin beta in the absence of importin alpha.