Instructions: In this task, you are given a sentence. You are expected to recognize the name of gene or protein. Although there might be several correct answers, you need to write one of them.
Input: Electrophoretic mobility - shift assays with nuclear extracts from COS - 1 cells transfected with expression vectors for SMADs 1 - 5 indicate that SMAD3 forms a complex with a migration similar to that of the endogenous TGF - beta - specific complex observed in fibroblast extracts .
Output:
TGF - beta