Human cytomegalovirus-induced chromatin factors responsible for changes in template activity and structure of infected cell chromatin

Abstract

Human cytomegalovirus (HCMV) infection in human embryo lung cells caused rapid changes in conformation of chromatin as judged from circular dichroism (the ellipticity at 272 run) of the infected cell nuclei or chromatin determined at intervals after infection. The infection also caused a rapid increase in chromatin template activity determined by (i) the incorporation of [ 3H]UTP into RNA in the presence of saturating levels of E. coli RNA polymerase and (ii) the number of binding sites for ethidium bromide in chromatin. These conformational and functional changes did not occur when cycloheximide was present in the cultures or when cells were infected with UV-irradiated virus, suggesting the dependency of the chromatin changes on HCMV-coded functions expressed after infection. Chromatin reconstitution experiments in which NaCl extracts from HCMV-infected cell chromatin were added to uninfected cell chromatin and the reconstituted chromatin was subjected to the determination of ellipticity at 272 nm and dye-binding capacity showed that HCMV induced at least two chromatin factors; one responsible for an increase in ellipticity at 272 nm of chromatin was selectively extractable with 0.35 – 0.6 M NaCl from HCMV-infected cell chromatin and the other responsible for an increase in dye-binding capacity (corresponding to chromatin template activity) was extractable with 0.35 M NaCl. These chromatin factors had properties of DNA-binding proteins; the former was dissociated from DNA at 0.6 M NaCl and the latter at 0.35 M NaCl.