The Core Histone-binding Region of the Murine Cytomegalovirus 89K Immediate Early Protein

Department of Virology, Institute for Microbiology, University of Ulm, 7900 Ulm, Germany The gene regulatory immediate early protein, pp89, of murine cytomegalovirus interacts with both DNA-associated and isolated histones in vitro . We characterized the histone-binding region of pp89 and its cellular localization during cell division to examine the possible interaction between pp89 and chromatin. pp89 expressed constitutively in cell line BALB/c 3T3 IE1 does not interact with condensed chromatin. As observed in infected cells, pp89 is localized within the nucleus of cells during interphase but spreads throughout the cell plasma following degradation of the nuclear membrane during early mitosis. In late telophase, pp89 is reorganized within the nucleus. Analysis of pp89 deletion mutants and of fragments generated by cleavage at pH 2·5 revealed that the regions responsible for association with histone are located between amino acids 71 and 415, and are not identical with the domain that shows homology to histone H2B or the highly acidic carboxy-terminal region. A potential gene-activating role of the high affinity of pp89 for isolated histones and the low affinity for DNA-associated histones is discussed. Received 4 February 1991; accepted 25 April 1991.