Final answer:
GCN4 interacts with DNA and adds acetyl groups to histone tails through histone acetylation, promoting loose packing of nucleosomes and gene expression.
Step-by-step explanation:
When GCN4 interacts with DNA, it adds acetyl groups to the histone tails. This process is known as histone acetylation, which promotes loose packing of nucleosomes and opens the underlying DNA for transcription. In other words, histone acetylation allows transcription factors to bind to the DNA and activate gene expression.