A viral histone h4 joins to eukaryotic nucleosomes and alters host gene expression.
A viral histone H4 (CpBV-H4) is encoded in a polydnavirus, Cotesia plutellae bracovirus. Its predicted amino acid sequence is highly homologous to that of host insect histone H4 except for an extended N-terminal tail containing 38 amino acids with nine lysine residues. Its expression induces an immunosuppression of target insects by suppressing immune-associated genes, presumably through an epigenetic control. This study analyzed its molecular interaction with eukaryotic host nucleosomes and subsequent regulation of host gene expression. Purified recombinant CpBV-H4 could associate with nucleosomal components (H2A, H2B, H3, and H4) and form an octamer. Transient expression of CpBV-H4 in an insect, Tribolium castaneum, was performed by microinjection of a recombinant expression vector and confirmed by both reverse transcriptase PCR (RT-PCR) and immunoblotting assays. Under this transient expression condition, total RNAs were extracted and read by a deep-sequencing technique. Annotated transcripts were classified into different gene ontology (GO) categories and compared with those of control insects injected with a truncated CpBV-H4. Target genes manipulated by CpBV-H4 expression showing significant differences (fold changes > 10(9)) included all GO categories, including development and immune-associated genes. When the target genes were physically mapped, they were found to be scattered on entire chromosomes of T. castaneum. In addition, chromatin immunoprecipitation against CpBV-H4 determined 16 nucleosome sites (P < 10(-5)) of the viral histone incorporation, which were noncoding regions near DNA-binding and inducible genes. These findings suggest that the viral histone H4 alters host gene expression by a direct molecular interaction with insect nucleosomes.
Department of Bioresource Sciences, Andong National University, Andong, South Korea.
Rahul
R
Hepat
Ji-Joon
JJ
Song
Daeweon
D
Lee
Yonggyun
Y
Kim
D000818:Animals; D047369:Chromatin Immunoprecipitation; D044127:Epigenesis, Genetic; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D059014:High-Throughput Nucleotide Sequencing; D006657:Histones / Q000378:metabolism*; D054884:Host-Pathogen Interactions; D009707:Nucleosomes / Q000378:metabolism*; D018071:Polydnaviridae / Q000502:physiology*; D011485:Protein Binding; D014231:Tribolium / Q000821:virology; D014764:Viral Proteins / Q000378:metabolism*
D006657:Histones; D009707:Nucleosomes; D014764:Viral Proteins