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.
Q: Supershift assays showed no effect of the anti - Sp1 antibody on complex formation , whereas the anti - Sp3 antibody had a strong effect on protein . DNA complex formation , suggesting that Sp3 is one of the main factors binding to this Sp1 site .
A:
Sp1 site