The N domain of Smad7 is essential for specific inhibition of transforming growth factor-β (TGF-β) signaling. Smad7, an inhibitory Smad (I-Smad), is more effective than Smad6 in inhibiting TGF-β and bone morphogenetic protein (BMP) signaling. The study shows that the N domain of Smad7 is crucial for its inhibitory activity, particularly in targeting TGF-β signaling. The N domain determines the subcellular localization of I-Smads and enhances the interaction of Smad7 with TGF-β receptors, thereby increasing its inhibitory effect. The MH2 domain of Smad7 is also essential for inhibiting TGF-β and BMP signaling, but the N domain is necessary for efficient inhibition. The N domain of Smad7 interacts with its MH2 domain, facilitating interaction with TGF-β receptors and enhancing the inhibitory activity of the MH2 domain. The study also reveals that the N domain of Smad7 is important for the specific inhibition of TGF-β signaling, while the N domains of Smad6 and Smad7 are only partially conserved. The results indicate that the N domain of Smad7 plays a critical role in the specific inhibition of TGF-β signaling, and that the interaction between the N domain and the MH2 domain is essential for this function. The study also shows that the subcellular localization of I-Smads is determined by their N domains, and that Smad7 is more effective in inhibiting TGF-β signaling than Smad6. The findings suggest that the N domain of Smad7 is essential for its inhibitory activity in TGF-β signaling.The N domain of Smad7 is essential for specific inhibition of transforming growth factor-β (TGF-β) signaling. Smad7, an inhibitory Smad (I-Smad), is more effective than Smad6 in inhibiting TGF-β and bone morphogenetic protein (BMP) signaling. The study shows that the N domain of Smad7 is crucial for its inhibitory activity, particularly in targeting TGF-β signaling. The N domain determines the subcellular localization of I-Smads and enhances the interaction of Smad7 with TGF-β receptors, thereby increasing its inhibitory effect. The MH2 domain of Smad7 is also essential for inhibiting TGF-β and BMP signaling, but the N domain is necessary for efficient inhibition. The N domain of Smad7 interacts with its MH2 domain, facilitating interaction with TGF-β receptors and enhancing the inhibitory activity of the MH2 domain. The study also reveals that the N domain of Smad7 is important for the specific inhibition of TGF-β signaling, while the N domains of Smad6 and Smad7 are only partially conserved. The results indicate that the N domain of Smad7 plays a critical role in the specific inhibition of TGF-β signaling, and that the interaction between the N domain and the MH2 domain is essential for this function. The study also shows that the subcellular localization of I-Smads is determined by their N domains, and that Smad7 is more effective in inhibiting TGF-β signaling than Smad6. The findings suggest that the N domain of Smad7 is essential for its inhibitory activity in TGF-β signaling.