Relative localization of viroplasmic and endoplasmic reticulum-resident rotavirus proteins in infected cells - Brief report

Replication of rotaviruses, whose capsid is constituted by three concentric layers of proteins, occurs in large cytoplasmic inclusions, termed viropla sms. Subviral, double-layered particles bud from viroplasms to the adjacent endoplasmic reticulum (ER), where the outermost protein layer, formed by V P4 and VP7, is assembled. To better understand the morphogenetic process of the virus, we analyzed the relative distribution of viroplasmic and ER-res ident viral proteins. Using double immunostaining and confocal microscopy w e observed an extensive co-localization between the ER proteins NSP4 and VP 7, and the cytoplasmic protein VP4. These three proteins were found to be o rganized mostly as ring-like or semicircular structures in close associatio n with viroplasms, except for VP4 which displayed in addition, a filamentou s distribution. The observations reported in this study underscore the high ly organized nature of rotavirus morphogenesis.