Cover photograph (Copyright © 2006, American Society for Microbiology. All Rights Reserved.): Immunofluorescence staining of human fibroblast cells infected with the protozoan pathogen Toxoplasma gondii. Green indicates acetylated histone H3 lysine 18 in both host cell nuclei and parasite nuclei. Red is DAPI (4`,6`-diamidino-2-phenylindole) nuclear stain. The upper panels show wild-type T. gondii parasites and the lower panels show a clone lacking one of its two GCN5 family histone acetyltransferases (TgGCN5-A). The clone lacking TgGCN5-A remains capable of acetylating histone H3 at this residue in vivo. (See related article on p. 62.)