Showing papers by "Stephen D. Bell published in 2013"

The Minichromosome Maintenance Replicative Helicase

Abstract: The eukaryotic replicative helicase, the minichromosome maintenance (MCM) complex, is composed of six distinct, but related, subunits MCM(2-7) The relationship between the sequences of the subunits indicates that they are derived from a common ancestor and indeed, present-day archaea possess a homohexameric MCM Recent progress in the biochemical and structural studies of both eukaryal and archaeal MCM complexes are beginning to shed light on the mechanisms of action of this key component of the replisome

Electron cryotomography of ESCRT assemblies and dividing Sulfolobus cells suggests that spiraling filaments are involved in membrane scission

Abstract: The endosomal-sorting complex required for transport (ESCRT) is evolutionarily conserved from Archaea to eukaryotes. The complex drives membrane scission events in a range of processes, including cytokinesis in Metazoa and some Archaea. CdvA is the protein in Archaea that recruits ESCRT-III to the membrane. Using electron cryotomography (ECT), we find that CdvA polymerizes into helical filaments wrapped around liposomes. ESCRT-III proteins are responsible for the cinching of membranes and have been shown to assemble into helical tubes in vitro, but here we show that they also can form nested tubes and nested cones, which reveal surprisingly numerous and versatile contacts. To observe the ESCRT–CdvA complex in a physiological context, we used ECT to image the archaeon Sulfolobus acidocaldarius and observed a distinct protein belt at the leading edge of constriction furrows in dividing cells. The known dimensions of ESCRT-III proteins constrain their possible orientations within each of these structures and point to the involvement of spiraling filaments in membrane scission.

Functional interplay between a virus and the ESCRT machinery in Archaea

Abstract: Recently it has been discovered that a number of eukaryotic viruses, including HIV, coopt the cellular Endosomal Sorting Complex Required for Transport (ESCRT) machinery to affect egress from infected cells. Strikingly, the ESCRT apparatus is conserved in a subset of Archaea, including members of the genus Sulfolobus where it plays a role in cytokinesis. In the current work, we reveal that the archaeal virus Sulfolobus turreted icosahedral virus isolated from Yellowstone National Park's acidic hot springs also exploits the host ESCRT machinery in its replication cycle. Moreover, perturbation of normal ESCRT function abrogates viral replication and, thus, prevents establishment of a productive Sulfolobus turreted icosahedral virus infection. We propose that the Sulfolobus ESCRT machinery is involved in viral assembly within the cytoplasm and in escape from the infected cell by using a unique lysis mechanism. Our results support an ancient origin for viruses “hijacking” ESCRT proteins to complete their replication cycle and thus identify a critical host–virus interaction conserved between two domains of life.