Background
SMADs are members of the MAD-related family of molecules. MAD-related proteins are a  family of intracellular proteins that are essential components in the signaling pathways of the serine/threonine kinase receptors of the transforming growth factor beta superfamily (1).  SMADs can be divided into receptor-regulated SMADs (R-SMADs: SMAD1, SMAD2, SMAD5, SMAD8 and SMAD9), common-mediator SMAD (co-SMAD: SMAD4), and inhibitory SMADs (I-SMADs: SMAD6 and SMAD7).  SMAD1, SMAD5, SMAD8 and SMAD9 have high degrees of homology and antibodies are available that recognize sequences common to all of them.  SMAD8 and SMAD9 are typically used as alternate names for one another in the literature.  Human SMAD1 is a 465 amino acid protein; GenBank Accession No. AAP36050.1.  Human SMAD2 is a 467 amino acid protein; GenBank Accession No. AAC51918.1 Human SMAD3 is a 425 amino acid protein; GenBank Accession No. NP_005893.1 Human SMAD4 is a 552 amino acid protein GenBank Accession No. NP_005350.1. Human SMAD5 is a 465 amino acid protein; GenBank Accession No. AAC50791.1. Human SMAD6 is a 496 amino acid protein; GenBank Accession No. AAH12986.1  Human SMAD7 is a 426 amino acid protein; GenBank Accession No. AAB81354.1 Mouse SMAD8 is a 430 amino acid protein; GenBank Accession No. AAN85445.1 Human SMAD9 is a 430 amino acid protein; GenBank Accession No. NP_005896.1

Antigen
This antibody was developed against synthetic peptides corresponding to amino acids 186-199 (PSNRASTETYSTPA) and amino acids 509-523(PSNRASTETYSTPA) of human SMAD4 (GenBank Accession No. NP_005350.1).  These peptide sequences are specific to SMAD4, and have high homology to SMAD4 in multiple species. 

Application Notes
In A549, a 60 kDa band is observed.

Genebank Info (Protein)
NP_005350

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Reference
1. Topper,J.N., Cai,J., Qiu,Y., Anderson,K.R., et al. Vascular MADs: two novel MAD-related genes selectively inducible by flow in human vascular endothelium. Proc. Natl. Acad. Sci. U.S.A. 94 (17), 9314-9319 (1997).