The Structure of Adenovirus Chromatin in Infected Cells

Département de Microbiologie, Centre Hospitalier Universitaire de Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4 The structure of adenovirus chromatin in infected cells was studied by micrococcal nuclease digestion and hybridization with virus-specific probes. In the early phase of infection (5 h) a significant proportion of viral molecules was organized like actively transcribed cellular chromatin. As expected for a transcriptionally active population of molecules, even at high multiplicity of infection the nucleosomal repeating pattern was less distinct than in a transformed cell which contained the corresponding but less active genomic region. The observed repeating pattern in infected cells was unlikely to be due to integrated molecules since less than 0.07% of input genomes became associated with cellular DNA. After the onset of viral DNA replication, the pool of viral chromatin organized like cellular chromatin rapidly increased. In addition, newly replicated molecules also maintained the cellular chromatin-like organization as measured by [ 3 H]thymidine incorporation after the cessation of cellular DNA synthesis. These data suggest that newly replicated viral molecules are organized by histones into cell-like chromatin throughout the infection cycle. Coincident with the peak of viral DNA and core protein synthesis, and the decline of histone synthesis, the late, core-like non-repeating viral chromatin became dominant, increasingly obscuring the underlying repeating pattern. Experiments suggest that this late chromatin is destined for encapsidation, that the early chromatin persists and that viral core proteins do not displace histones on viral DNA. A model is proposed suggesting that transcription and type I replication occur on histone-condensed templates, while type II replication products late in infection are condensed by core proteins and are destined for encapsidation. Keywords: adenovirus chromatin, Southern blotting, micrococcal nuclease Present address: Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, U.S.A. Present address: Institute of Microbiology, University Medical School, Szeged, 6720, Dom tér 10, Hungary. Present address: Department of Virology, Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada. || Present address: Institute of Microbiology, Semmelweis, University of Medicine, Budapest, 1089, Nagyvarad tér 4, Hungary. Received 16 April 1985; accepted 12 August 1985.