Polyomavirus small T antigen controls viral chromatin modifications through effects on kinetics of virus growth and cell cycle progression.
Minichromosomes of wild-type polyomavirus were previously shown to be highly acetylated on histones H3 and H4 compared either to bulk cell chromatin or to viral chromatin of nontransforming hr-t mutants, which are defective in both the small T and middle T antigens. A series of site-directed virus mutants have been used along with antibodies to sites of histone modifications to further investigate the state of viral chromatin and its dependence on the T antigens. Small T but not middle T was important in hyperacetylation at major sites in H3 and H4. Mutants blocked in middle T signaling pathways but encoding normal small T showed a hyperacetylated pattern similar to that of wild-type virus. The hyperacetylation defect of hr-t mutant NG59 was partially complemented by growth of the mutant in cells expressing wild-type small T. In contrast to the hypoacetylated state of NG59, NG59 minichromosomes were hypermethylated at specific lysines in H3 and also showed a higher level of phosphorylation at H3ser10, a modification associated with the late G(2) and M phases of the cell cycle. Comparisons of virus growth kinetics and cell cycle progression in wild-type- and NG59-infected cells showed a correlation between the phase of the cell cycle at which virus assembly occurred and histone modifications in the progeny virus. Replication and assembly of wild-type virus were completed largely during S phase. Growth of NG59 was delayed by about 12 h with assembly occurring predominantly in G(2). These results suggest that small T affects modifications of viral chromatin by altering the temporal coordination of virus growth and the cell cycle.
Dahl
Jean
J
Department of Pathology, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA.
Chen
H Isaac
HI
George
Michael
M
Benjamin
Thomas L
TL
D000107:Acetylation; D019943:Amino Acid Substitution; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle; D002843:Chromatin / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D006657:Histones / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D041681:NIH 3T3 Cells; D011120:Polyomavirus / Q000235:genetics / Q000254:growth & development*; D015398:Signal Transduction / Q000235:genetics; D019065:Virus Assembly / Q000502:physiology*; D014779:Virus Replication / Q000502:physiology*
D000952:Antigens, Polyomavirus Transforming; D002843:Chromatin; D006657:Histones