Given the task definition and input, reply with output. 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 understand the mechanisms underlying the cell - type - specific expression of this gene , we have characterized the regulatory functions and the DNA - protein interactions of the 5 ' - flanking region of the mouse perforin gene ( Pfp ) .

mouse perforin gene