The adenovirus genome forms chromatin-like structure with viral core proteins. This complex supports only a low level of transcription in a cell-free system, and thus core proteins have been thought to be negative factors for transcription. The mechanism how the transcription from the viral DNA complexed with core proteins is activated in infected cells remains unclear. Here, we found that both core proteins and histones are bound with the viral DNA in early phases of infection. We also found that acetylation of histone H3 occurs at the promoter regions of viral active genes in a transcription-independent manner. In addition, when a plasmid DNA complexed with core proteins was introduced into cells, core proteins enhanced transcription. Knockdown of TAF-I, a remodeling factor for viral core protein–DNA complexes, reduces the enhancement effect by core proteins, indicating that core proteins positively regulate viral transcription through the interaction with TAF-I. We would propose a possible mechanism that core proteins ensure transcription by regulating viral chromatin structure through the interaction with TAF-I.

Myogenic progenitor/stem cells retain their skeletal muscle differentiation potential by maintaining myogenic transcription factors such as MyoD. However, the mechanism of how MyoD expression is maintained in proliferative progenitor cells has not been elucidated. Here, we found that MyoD expression was reduced at the mRNA level by cell cycle arrest in S and G2 phases, which in turn led to the absence of skeletal muscle differentiation. The reduction of MyoD mRNA was correlated with the reduced expression of factors regulating RNA metabolism, including methyltransferase like 3 (Mettl3), which induces N6-methyladenosine (m6A) modifications of RNA. Knockdown of Mettl3 revealed that MyoD RNA was specifically downregulated and that this was caused by a decrease in processed, but not unprocessed, mRNA. Potential m6A modification sites were profiled by m6A sequencing and identified within the 5′ untranslated region (UTR) of MyoD mRNA. Deletion of the 5′ UTR revealed that it has a role in MyoD mRNA processing. These data showed that Mettl3 is required for MyoD mRNA expression in proliferative myoblasts.

Inside the adenovirus virion, the genome forms a chromatin-like structure with viral basic core proteins. Core protein VII is the major DNA binding protein and was shown to remain associated with viral genomes upon virus entry even after nuclear delivery. It has been suggested that protein VII plays a regulatory role in viral gene expression and is a functional component of viral chromatin complexes in host cells. As such, protein VII could be used as a maker to track adenoviral chromatin complexes in vivo. In this study, we characterize a new monoclonal antibody against protein VII that stains incoming viral chromatin complexes following nuclear import. Furthermore, we describe the development of a novel imaging system that uses Template Activating Factor-I (TAF-I/SET), a cellular chromatin protein tightly bound to protein VII upon infection. This setup allows us not only to rapidly visualize protein VII foci in fixed cells but also to monitor their movement in living cells. These powerful tools can provide novel insights into the spatio-temporal regulation of incoming adenoviral chromatin complexes.