Adenoviral chromatin organization primes for early gene activation

Abstract

Within the virion, adenovirus DNA associates with the virus-encoded, protamine-like structural protein pVII. Whether this association is organized, and how genome packaging changes during infection and subsequent transcriptional activation is currently unknown. Here, we combined RNA-seq, MNase-seq, ChIP-seq and single genome imaging during early adenovirus infection to unveil the structure- and time-resolved dynamics of viral chromatin changes as well as their correlation with gene transcription. Our MNase mapping data indicates that the viral genome is arranged in precisely positioned nucleoprotein particles (Adenosomes), like nucleosomes. We identified 238 Adenosomes, being positioned by a DNA sequence code and protecting about 60 to 70bp of DNA. The incoming genome is more accessible at early gene loci that undergo additional chromatin de-condensation upon infection. Histone H3.3 containing nucleosomes specifically replace pVII at distinct genomic sites and at the transcription start sites of early genes. Acetylation of H3.3 is predominant at the transcription start sites, preceding transcriptional activation. Based on our results we propose a central role for the viral pVII nucleoprotein-architecture, which is required for the dynamic structural changes during early infection, including the regulation of nucleosome assembly prior to transcription initiation. Our study thus may aid the rational development of recombinant adenoviral vectors exhibiting sustained expression in gene therapy.