KAT5 or K (lysine) acetyltransferase 5 is a signaling protein that belongs to the MYST family of histone acetyl transferases (HATs). KAT5 was originally isolated as an HIV-1 TAT-interactive protein that plays an important role in regulating chromatin remodeling, transcription and other nuclear processes by acetylating histone and nonhistone proteins (1). KAT5 protein is a histone acetylase that is involved in DNA repair and apoptosis and plays an important role in signal transduction. KAT5 acts as a cofactor of TAT that is involved in the regulation of HIV gene expression. KAT5 is also a co-regulator of transcription factors that either promote or suppress tumorigenesis (2).