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

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.