Stephen Bell

Stephen Bell

Professor, Biology

  • stedbell@indiana.edu
  • (812) 856 2331
  • Simon Hall 405A
  • Office Hours
    M-F
    By Appointment Only

Education

  • Postdoctoral Fellow, Gurdon Inst. Cambridge, UK, 1996-2001
  • Postdoctoral Fellow, University of Glasgow, 1992-1995
  • Ph.D., Molecular Biology, University of Glasgow, Scotland, 1992
  • B.Sc., Molecular Biology, Glasgow University, Scotland

About

Lab

Simon Hall 405
(812) 856-0747
Bell Lab website

Awards

EMBO Fellow
Alexander M Cruikshank Awardee
American Academy of Microbiology Fellow

Research

Overview and context

In the late 1970s Carl Woese discovered that living organisms on Earth could be classified into one of three distinct domains, Eukarya, Bacteria and Archaea. In the time following that pivotal discovery, it has become apparent that, although morphologically resembling bacteria, the archaea in fact possess a number of molecular features more reminiscent of eukarya than bacteria. More specifically, the information processing pathways in archaea form a simplified version of the eukaryotic apparatus. Our work has primarily focussed on members of the genus Sulfolobus. In particular we have studied S. solfataricus and S. acidocaldarius. These species are hyperthermophilic acidophilic aerobes (they grow at 80°C and at pHs between 2 and 4). The hyperthermophilicity of the organisms is mirrored by an innate thermostability of the proteins that they encode. This greatly facilitates purification of native and recombinant proteins. There are also a growing number of genetic tools available for these species, further adding to their utility as model organisms.

DNA replication

DNA replication is a complex multi-step process involving the coordinated interplay of many proteins. During evolution, two distinct sets of cellular DNA replication proteins have evolved, one used by bacteria and a core machinery common to archaea and eukaryotes. In general the archaeal apparatus is a simplified version of that in eukaryotes, making Archaea a useful model system. We have mapped 3 origins of replication in the single chromosome of Sulfolobus and have characterized the interplay of initiator proteins with the origins. In addition, we are investigating the architecture of the replication fork assembly. In particular we are interested in the interplay between architectural and enzymatic components of the Okazaki fragment maturation machinery. Additionally, we have studied how replication termination is effected in Sulfolobus. Beyond the core replication architectures, we are interested in the twin processes of sister chromatid cohesion and chromosome dimer resolution in Sulfolobus.

Transcription

As with DNA replication, the archaeal transcription apparatus is a slimmed down version of the eukaryotic machinery. The archaeal RNA polymerase is able to initiate transcription in vitro with the aid of just two general transcription factors, TBP and TFB. In collaboration with Nicola Abrescia (Bilbao) we are investigating the archaeal transcription apparatus using a combination of structural analyses and next generation sequencing technologies.

Cell Division

Cell division in Eukaryotes and most Bacteria and Archaea is dependent on proteins in the near ubiquitous FtsZ/Tubulin and MreB/Actin superfamilies. However, the genomes of Sulfolobus and a number of other crenarchaea notably lack genes for these proteins. We have identified Sulfolobushomologs of the eukaryotic ESCRT system as key players in Sulfolobus cell division. The ESCRT proteins in eukaryotes play a diverse variety of roles including endosome sorting, membrane abscission during cytokinesis and is a system that is highjacked by viruses, including HIV and Ebola, to exit from cells. The Sulfolobus ESCRT system contains a limited subset of the eukaryal machinery. In particular, the early components of the eukaryal machinery, that define positioning of the apparatus lack clear orthologs in Sulfolobus. In our recent work, we have identified the factor responsible for recruiting Sulfolobus ESCRT-III to membranes at mid-cell.

Research areas:

Chromatin, Chromosomes, and Genome Integrity
Evolution
Microbial Cell Biology and Environmental Responses

Publications

J. Yan, T.R. Beattie, A. Rojas, K. Schermerhorn, T. Gristwood, S. Albers, P. Roversi, A. Gardner, N.G. Abrescia and S.D Bell. 2017. Identification and characterization of a heterotrimeric archaeal DNA polymerase holoenzyme. Nature Communications, 8, 15075.

Y. Xu, T. Gristwood, B. Hodgson, J.C. Trinidad, S.V. Albers and S.D. Bell. (2016) Archaeal orthologs of Cdc45 and GINS interact form a stable complex that stimulates the helicase activity of MCM. Proc. Natl. Acad. Sci. (USA) 113, 13390-13395.

R.Y. Samson, P Abeyrathne and S.D. Bell (2016) Mechanism of archaeal MCM helicase recruitment to DNA replication origins. Molecular Cell, 61, 287-296.

See all publications