Cover photograph (Copyright © 2005, American Society for Microbiology. All Rights Reserved.): Targeting of retroviral DNA integration in the chicken genome. The box behind the rooster shows ideograms of the chicken chromosomes, indicating sites of retroviral integration by avian sarcoma-leukosis virus (red lollipops) and human immunodeficiency virus (blue lollipops). The locations of chicken endogenous retroviral sequences are also indicated (purple shading for endogenous retrovirus group L; green shading for endogenous retrovirus group K). (Cover by Jamie Simon, Stephen Barr, Jeremy Leipzig, and Frederic Bushman.) (See related article on page 10852.)