Progeny Varicella-Zoster Virus Capsids Exit the Nucleus but Never Undergo Secondary Envelopment during Autophagic Flux Inhibition by Bafilomycin A1

Girsch, James H.; Walters, Katherine; Jackson, Wallen; Grose, Charles

frequently than was seen in infected cells without BAF treatment. Although many of these particles were aberrant in appearance, a variety of similarly aberrant VZV particles have been seen previously in VZV-infected cultures (20) . Capsids exited the ONM and were detected within the cytoplasm, often adjacent to Golgi-derived vacuoles. When we surveyed prior electron microscopy investigations of the VZV infectious cycle, we noted that the virtual absence of VZV capsids in the cytoplasm of untreated infected cells (human amnion cells, human fibroblasts, and human melanoma cells) had been documented by 6 different laboratories over the past 50 years (21, 22, (26) (27) (28) (29) . Thus, BAF treatment led to an accumulation of capsids in the cytoplasm. We also attempted to find evidence for wrapping of the capsids within the TGN but were unsuccessful after an extensive search. Instead, we found a few Golgi-derived vacuoles containing viral particles that resembled light particles. The particles contained an envelope but no capsid; the particles also varied considerably in diameter. We failed to find prototypical enveloped capsids (virions 200 nm in diameter) within individual vesicles in the cytoplasm. Based on the above-mentioned observations, we propose that secondary envelopment is blocked by BAF treatment. In other words, capsids are transported to the region of the TGN, but the formation of the compartment required for tegumentation and/or envelopment of incoming capsids is disrupted in BAF-treated cells. The above-mentioned VZV data are also supported by models of HSV assembly (30) .