Cover photograph (Copyright © 2006, American Society for Microbiology. All Rights Reserved.): Drosophila polytene chromosomes were visualized with DAPI (4`,6`-diamidino-2-phenylindole; blue) and stained with antibodies against host cell factor (dHCF; red) and dAda3 (green). The three signals were merged to visualize regions where dAda3 and dHCF colocalize (yellow). These bands correspond to binding sites for the novel ATAC histone acetyltransferase complex. (See related article on p. 871.)