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.

To examine the biochemical mechanism of Tax1 transactivation , we have developed an in vitro transactivation assay in which wild - type Tax1 is able to specifically transactivate a polymerase II promoter through upstream Tax1 - responsive elements .
polymerase II