SRA

A viral histone H4 (= CpBV-H4) is encoded in a polydnavirus, Cotesia plutellae bracovirus. Its predicted amino acid sequence is highly homologous to host insect histone H4 except an prolonged N-terminal tail containing 38 amino acids with nine lysine residues. Its expression induces immunosuppression of target insects by suppressing immune-associated genes presumably through an epigenetic control. This study determined its molecular interaction with host nucleosomes and identified its target genes to be altered in their transcription by an Illumina RNASeq. Reassociation of nucleosome components with a recombinant CpBV-H4 produced octamers containing each monomer of H4 and CpBV-H4 plus dimers of H2A, H2B, and H3. Transient expression of CpBV-H4 in a model insect, Tribolium castaneum, was performed by microinjection of a recombinant expression vector and confirmed by RT-PCR and immunoblotting. Under this transient expression condition, total RNAs were extracted and read with an Illumina HiSeq 2000. Annotated transcripts were classified into different GO categories and compared with those of control insects injected with a nonrecombinant expression vector. Target genes manipulated by CpBV-H4 expression showing significant differences (P < 10-9) included all GO categories including immune-associated genes. When the target genes were physically mapped, they were scattered on entire chromosomes of T. castaneum. Interestingly, half of target genes were matched to sites of chromatin immunoprecipaton of CpBV-H4. These suggest that the viral histone H4 alters host gene expression by a direct molecular interaction with target insect nucleosomes without clear specificity.