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A Jun-binding protein related to a putative tumor suppressor
1Department of Microbiology, University of Southern California School of Medicine, Los Angeles.
Abstract:
A lambda gt11 cDNA library of chicken embryo fibroblasts was screened with biotinylated Jun protein to identify Jun-binding clones. Eight such clones were isolated; one contains a gene referred to as jif-1 that is homologous to the putative tumor suppressor gene QM. jif-1 codes for a protein of 25 kDa that binds to the leucine zipper of viral and cellular Jun. The Jif-1 protein also binds to itself. Jif-1 does not contain a leucine zipper, and it does not bind to the 12-O-tetradecanoylphorbol 13-acetate response element DNA sequence. Complex formation of Jif-1 with Jun inhibits DNA binding and reduces transactivation by Jun. Addition of Fos protein to Jun-Jif-1 complexes restores DNA-binding activity. These observations suggest that Jif-1 is a negative regulator of Jun.
Insights
Researchers identified Jif-1, a protein that negatively regulates Jun, a key protein in cell regulation. Jif-1 binds to Jun, inhibiting its DNA binding and transactivation functions.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncogenesis
Background:
- Jun is a transcription factor involved in cellular regulation and oncogenesis.
- Identifying regulators of Jun activity is crucial for understanding cellular processes.
- The Jun-binding factor 1 (Jif-1) was investigated for its role in Jun regulation.
Purpose of the Study:
- To identify and characterize proteins that bind to Jun.
- To elucidate the functional role of the identified Jun-binding factor, Jif-1.
- To determine if Jif-1 acts as a regulator of Jun activity.
Main Methods:
- Screening of a chicken embryo fibroblast cDNA library using biotinylated Jun protein.
- Isolation and characterization of Jun-binding clones.
- Protein-protein interaction assays (Jif-1 self-binding, Jun-Jif-1 complex formation).
- DNA-binding assays and transactivation studies involving Jun, Jif-1, and Fos proteins.
Main Results:
- Eight Jun-binding clones were isolated, including one containing the jif-1 gene.
- Jif-1 protein (25 kDa) binds to the leucine zipper of viral and cellular Jun, and also self-binds.
- Jif-1 does not possess a leucine zipper and does not bind to specific DNA sequences.
- Complex formation with Jun inhibits Jun's DNA binding and reduces its transactivation activity.
- Fos protein addition to Jun-Jif-1 complexes restores DNA-binding activity.
Conclusions:
- Jif-1 is a novel protein that interacts with Jun.
- Jif-1 functions as a negative regulator of Jun activity by inhibiting DNA binding and transactivation.
- The interaction between Jif-1, Jun, and Fos suggests a complex regulatory mechanism for Jun-mediated gene expression.