Catalytic component of the histone acetylase B (HAT-B) complex. Acetylates 'Lys-12' of free histone H4 in the cytoplasm. The complex is also found in the nucleus, however it is not certain that it modifies histone H4 when packaged in chromatin. Histone H4 'Lys-12' acetylation is required for telomeric silencing. Has intrinsic substrate specificity that modifies lysine in recognition sequence GXGKXG. Involved in DNA double-strand break repair. acetyl-CoA + L-lysyl-[protein] = CoA + H(+) + N(6)-acetyl-L-lysyl-[protein] Component of the HAT-B complex composed of at least HAT1 and HAT2. In the cytoplasm, this complex binds to the histone H4 tail. In the nucleus, the HAT-B complex has an additional component, the histone H3/H4 chaperone HIF1. Belongs to the HAT1 family.