Histone acetyltransferases (HATs) are enzymes that play a crucial role in the regulation of gene expression. They add acetyl groups to histone proteins, which are key components of chromatin in the cell nucleus. This acetylation process reduces the positive charge of histones, leading to a more relaxed chromatin structure that allows for easier access to DNA by transcription machinery. By modifying histones, HATs facilitate the transcription of specific genes, promoting cellular functions and responses. Dysregulation of HAT activity can contribute to various diseases, including cancer, making them important targets for therapeutic research and drug development.