Detailed 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.
Q:  In S . cerevisiae , there is evidence that Sir3p ( hence the SIR complex ) has much higher affinity to unacetylated histone H4 than acetylated H4 ( 5 ) .
A:
S . cerevisiae