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At least three subdomains of v-erbA are involved in its silencing function
K Busch1, B Martin, A Baniahmad
1Laboratoire de Biologie Moléculaire et de Génie Génétique, Université de Liège, Sart-Tilman, Belgium.
Abstract:
Several members of the thyroid hormone receptor (TR) family are able to switch from a transcriptional repressor to a transcriptional activator upon binding of their ligand. The oncogene v-erbA is a variant form of the TR unable to bind hormone and thus acts as a constitutive repressor. We demonstrate, using fusion proteins between the DNA-binding domain of the yeast factor GAL4 and the silencing domains of v-erbA and TR beta, that point mutations in three different regions severely affect their repression function. Furthermore, the three regions, each as an inactive fusion protein with the GAL4 DNA-binding domain, restore silencing activity when assembled on the same promoter. These observations define at least three silencing subdomains, SSD1-SSD3, which are involved in the silencing function of v-erbA. We propose a model in which full silencing activity is brought about by the combined interaction of each silencing subdomain with corepressors and/or basal transcription factors.
Insights
The oncogene v-erbA, a variant thyroid hormone receptor (TR), functions as a repressor. Mutations in three key regions impair its silencing ability, suggesting distinct silencing subdomains are crucial for v-erbA
Area of Science:
- Molecular Biology
- Genetics
- Endocrinology
Background:
- Thyroid hormone receptors (TRs) modulate gene expression, acting as repressors or activators.
- The oncogene v-erbA, a mutated TR, constitutively represses transcription due to its inability to bind ligands.
Purpose of the Study:
- To identify regions within v-erbA responsible for its transcriptional repression activity.
- To elucidate the mechanism of silencing mediated by v-erbA.
Main Methods:
- Utilized GAL4 DNA-binding domain fusion proteins to isolate and test silencing domains of v-erbA and TR beta.
- Introduced point mutations in specific regions of v-erbA to assess their impact on repression function.
- Reconstituted silencing activity by assembling mutated silencing subdomains on the same promoter.
Main Results:
- Identified at least three distinct silencing subdomains (SSD1-SSD3) within v-erbA.
- Point mutations in these subdomains significantly impaired the repression function of v-erbA.
- Individual silencing subdomains, when fused to the GAL4 DNA-binding domain, could restore silencing activity upon co-expression.
Conclusions:
- v-erbA employs at least three independent silencing subdomains for its function.
- Full transcriptional repression by v-erbA likely results from the coordinated interaction of these subdomains with corepressors and basal transcription factors.