First , it allows Smad4 to reach its peak of transcriptional activity by activating a growth factor - regulated transcription activation domain located in the Smad4 linker region , SAD ( Smad - Activation Domain ) .
This phosphorylation event has a dual effect on Smad4 activity .
First , it allows Smad4 to reach Smad4 's peak of transcriptional activity by activating a growth factor - regulated transcription activation domain located in Smad4 Smad4 linker region , SAD ( Smad - Activation Domain ) .
This phosphorylation event has a dual effect on Smad4 activity .