SMAD (protein)

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SMAD's are a class of proteins that modulate the activity of transforming growth factor beta ligands. There are three classes of SMAD: 1) receptor regulated SMAD (R-SMAD) which include SMAD1, SMAD2, SMAD3, SMAD5 and SMAD9; 2)the coSMAD SMAD4; and 3) inhibitory SMAD (I-SMAD) which include SMAD6 and SMAD7. The SMAD's form complexes, often with other SMAD's enter, the nucleus and serve as transcription factors.

[edit] Nomenclature

The SMAD proteins are homologs of both the drosophila protein, mothers against decapentaplegic (MAD) and the C. elegans protein SMA. The name is a combination of the two. During Drosophila research, it was found that a mutation in the gene, MAD, in the mother, repressed the gene, decapentaplegic, in the embryo. The phrase "Mothers against" was added since mothers often form organizations opposing various issues eg. Mothers Against Drunk Driving or (MADD).

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