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: We have studied the events underlying cap formation using mice bearing a null mutation in vav ( vav - / - ) , a gene that encodes a guanine - nucleotide exchange factor for the GTPase Rac .
A:
GTPase Rac