ASSEMBLY OF ADENOVIRUS-SPECIFIC NUCLEAR INCLUSIONS IN LYTICALLY INFECTED HELA-CELLS - AN ULTRASTRUCTURAL AND CYTOCHEMICAL STUDY

Adenoviruses (Ads) are nuclear DNA viruses that remodel host nuclear s tructure and function and induce formation of a variety of nuclear inc lusions within which Ad DNA is replicated and transcribed. In this stu dy, we have examined inclusion assembly by electron microscopy of samp les stained conventionally or with bismuth to detect phosphoproteins. Small dense fibrillar bodies (DFBs) appeared very early associated wit h interchromatin granule (ICG) clusters. Somewhat later, similar DFBs lay near amorphous, loosely fibrillar structures that were moderately electron dense and showed little bismuth deposition. These clear fibri llar bodies (CFBs) enlarged and DFBs became embedded in their surface. At later stages, CFBs and DFBs were again dissociated. DFBs seen very early were poor in phosphoproteins, but later DFBs, whether embedded in the CFBs or lying near them, were intensely bismuth stained. DFBs a nd CFBs were less prominent once assembled virions were seen. At this late stage, virions were generally associated with moderately dense, s lightly bismuth positive, irregularly shaped fibrillar inclusions that have previously been identified as viral genome storage sites. In add ition, very dense fibrillar bodies, consisting usually of an electron- dense fibrillar shell and a less dense fibrogranular core, were observ ed at all but the earliest stages of infection, often at some distance from CFBs. There was also a major reorganization of host components d uring infection, including chromatin condensation, reduction of nucleo lar volume and aggregation of the fibrillar regions at the nucleolar s urface, and increased prominence of ICG clusters. A model is proposed for the assembly of Ad replication factories.