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Leucine zippers of fos, jun and GCN4 dictate dimerization specificity and thereby control DNA binding
1Department of Biochemistry, New York University Medical Center, New York 10016.
Abstract:
The products of the fos and jun protooncogenes form a stable heterodimer which binds to the TPA-responsive element (TRE) TGACTCA with high affinity. These two proteins, together with the yeast GCN4 protein, belong to a growing family of transcription factors, including FosB, Fra1, JunB and JunD, whose members share a highly conserved DNA-binding domain. This domain is composed of two structures: a basic motif, which is thought to bind directly to DNA; and a leucine zipper, which provides a dimerization interface. Although this domain is highly conserved in Fos, Jun and GCN4, each of these three proteins has very different relative affinities for the TRE. To understand these differences, we used 'domain-swapping' experiments designed to test the relative contributions of the basic motif and the leucine zipper to TRE-binding affinity. Here we show that fos, jun and GCN4 have different affinities for the TRE due to differences in the hetero- or homo-dimerization capacity of their leucine zipper domains; the basic motifs of these three proteins have comparable DNA binding potential. These results indicate that leucine zippers control the types of protein complexes which can associate with a TRE and regulate gene expression.
Insights
Transcription factors Fos and Jun form dimers that bind DNA. Differences in their leucine zipper domains, not DNA-binding motifs, dictate binding affinity and gene regulation.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Fos and Jun proto-oncogenes encode transcription factors that form heterodimers.
- These dimers bind the TPA-responsive element (TRE) with high affinity.
- A conserved DNA-binding domain, comprising a basic motif and a leucine zipper, is shared among Fos, Jun, and yeast GCN4.
Purpose of the Study:
- To investigate the structural basis for differential TRE-binding affinities among Fos, Jun, and GCN4.
- To determine the relative contributions of the basic motif and leucine zipper to DNA-binding affinity.
Main Methods:
- Utilized 'domain-swapping' experiments to analyze protein-DNA interactions.
- Compared DNA-binding potential of basic motifs and dimerization capacity of leucine zippers.
Main Results:
- The basic motifs of Fos, Jun, and GCN4 exhibit comparable DNA-binding potential.
- Differences in TRE-binding affinity are attributed to variations in the dimerization capacity of leucine zipper domains.
- Leucine zippers control the formation of protein complexes that bind TREs.
Conclusions:
- Leucine zippers play a critical role in regulating the specificity of transcription factor binding to TREs.
- This mechanism influences the regulation of gene expression by Fos-Jun family proteins.