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What are SMAD transcription factors and how do they regulate transcription?
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Smad proteins are transcription factors that are responsible for the regulation of the major cytokine pathway called the TGFBeta pathway. The Smad transcription factors function in the activation, deactivation, nucleocytoplasmic dynamics, and assembly of transcriptional complexes. Understanding the mechanisms of the Smad transcription factors is crucial to understanding the cytokine TGFBeta regulation.
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Introduction to SMAD protein
Smad proteins are transcription factors that regulate the most common cytokine signalling pathways in metazoan called the transforming growth factors-B (TGFB) pathway. TGFB pathway have a strong effect in regulating cell division, differentiation, migration, adhesion, organization, and death. The Smad protein is a transcription factors at the core of this TGFB signalling pathway. (1) The TGFB induces membrane receptors to directly activate Smad proteins that form transcriptional complexes to control target genes. These Smad complexes can activate and repress hundred of genes at the same time in the same cell. The anchor protein capture Smad proteins for presentation to activated receptor. Receptor mediated phosphorylation at the C terminus of Smad allow the accumulation of Smad proteins in the nucleus and the assembly of the Smad complex. (1) The Smad complex binds different DNA binding cofactors that target different genes. They also influence the recruitmet of either transcriptional coactivator and corepressors. The dephosphorylation of Smad terminate the TGFB signaling pathway.(1)
A SMAD is a type of protein, which is 500 amino acids long and deemed a transcription factor.
You can also mentioned that SMAD contain two globular domains. It has an N-terminal domain or MH1 domans and a C-terminal domain conserved in all Smad proteins. SMAD protein use the MH1 domain to bind to DNA and that is how it is a transcription factor.
Consequently SMADs are able to facilitate the activation or repression of genes and are accordingly heavily involved in cell proliferation, cell growth, apoptosis and differentiation. The SMADs regulatory action occurs in the nucleus, where the SMAD complex binds to the complimentary target areas of DNA and ...
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