Official websites use. Share sensitive information only on official, secure websites. The assembly and release of retrovirus particles from the cell membrane is directed by the Gag polyprotein.
The Gag protein of Rous sarcoma virus RSV traffics through the nucleus prior to plasma membrane localization. To gain insight into the properties of the RSV Gag protein within the nucleus, we examined the subnuclear localization and dynamic trafficking of RSV Gag. Fluorescence recovery after photobleaching FRAP demonstrated that the nucleolar fraction of Gag was highly mobile, indicating that the there was rapid exchange with Gag proteins in the nucleoplasm.
Nucleoli are distinct subnuclear compartments historically known for their central role in ribosome biogenesis Boisvert et al. The nucleolus contains three regions based on their appearance by electron microscopy: the fibrillar center FC , where rRNA transcription occurs; the dense fibrillar component DFC surrounding the FC, where rRNAs are processed and ribosomal proteins are localized; and the outermost layer, the granular component GC , which is the site of further rRNA processing and ribosomal subunit assembly.
Accordingly, the nucleolus contains many factors involved in RNA metabolism and ribonucleoprotein complex formation. In addition, proteomic analyses identified more than proteins in nucleoli Andersen et al. Through these studies, it has become apparent that the nucleolus is a key regulator of critical cellular processes in addition to ribosomal subunit assembly. Some viruses disrupt nucleolar architecture [e. Other viruses, such as poliovirus, arterivirus, and human immunodeficiency virus type 1 HIV-1 , disrupt nontraditional nucleolar functions and deregulate the cell cycle to enhance virus replication Miyazaki et al.
Many viral proteins that localize to nucleoli are capsid and nucleocapsid proteins that bind to viral genomes and direct virus particle assembly Matthews et al. Most of these proteins bind RNA, so nucleolar localization has been assumed to be a consequence of the high concentration of RNA in nucleoli.
