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The basic-helix-loop-helix-PAS orphan MOP3 forms transcriptionally active complexes with circadian and hypoxia
J B Hogenesch1, Y Z Gu, S Jain
1Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, Chicago, IL 60611, USA.
Summary
MOP3 acts as a dimerization partner for bHLH-PAS proteins, forming complexes that bind DNA and regulate transcription. These interactions are crucial for gene expression, particularly in response to cellular hypoxia.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- The basic-helix-loop-helix (bHLH)-PER-ARNT-SIM (PAS) superfamily regulates diverse biological processes.
- Understanding dimerization partners is key to elucidating transcriptional regulation mechanisms.
Purpose of the Study:
- To identify and characterize MOP3 as a dimerization partner for bHLH-PAS proteins.
- To determine the DNA-binding specificities and transcriptional activity of MOP3-containing heterodimers.
- To investigate the role of MOP3 in hypoxia-inducible gene expression.
Main Methods:
- Co-immunoprecipitation to assess protein-protein interactions.
- DNA selection assays to identify binding sites.
- Transient transfection and luciferase reporter assays to measure transcriptional activity.
- Analysis of MOP3 mRNA expression patterns in various tissues.
Main Results:
- MOP3 forms heterodimers with MOP4, CLOCK, HIF1alpha, and HIF2alpha.
- The MOP3-MOP4 heterodimer binds a CACGTGA DNA element, activating transcription.
- The MOP3-HIF1alpha heterodimer binds a TACGTGA DNA element, activating transcription and responding to hypoxia.
- MOP3 mRNA expression overlaps with its partners in multiple tissues.
Conclusions:
- MOP3 is a versatile dimerization partner for bHLH-PAS proteins, influencing transcriptional regulation.
- MOP3-containing heterodimers exhibit specific DNA-binding preferences and transcriptional activities.
- MOP3 plays a role in the hypoxia response pathway through its interaction with HIF proteins.