Faculty of Biological Sciences

Dr Christopher Thomas

BA, MA, Oxford; PhD, Leicester
School of Molecular and Cellular Biology

Background: Postdoctoral work at the Department of Biochemistry, University of Leicester; Wellcome Career Development Fellowship awarded 1994; moved to University of Leeds in 1995. Appointed Lecturer in 1998.

Contact:  Miall 6.02, +44(0) 113 34 33040, email address for  

You can read more about Dr Thomas's interests here:

Figure 1: The Rep proteins form specific homodimers prior to initiation of replication

Figure 2: Accessory protein MobC is required for MobA to cleave at oriT

Research Interests

Replication- and conjugation-specific proteins and the maintenance of extrachromosomal DNA

Bacterial resistance to antibiotics is often conferred by the presence of plasmids, or extrachromosomal DNA elements. Small plasmids of Gram positive organisms (such as Staphylococcus aureus) typically replicate via a 'rolling circle' mechanism, following cleavage of one DNA strand by a replication initiator protein. The mechanism of this process is related to that used by type-I topoisomerases and other replication initiators such as the gene II protein of bacteriophage M13.

The RepD protein initiates replication of plasmid pC221. We have characterised a new sequence motif at the active site of RepD, enabling it to carry out both DNA cleavage and religation reactions without added ATP. This motif does not, however, determine the dimerisation properties of the protein, which we are currently refining via domain swapping and site-directed mutagenesis experiments. RepD also recruits the PcrA helicase to the origin of replication, which serves to separate the DNA strands permitting replication. This interaction also stimulates the processivity of the helicase; we are investigating this mechanism using cloned RepD and PcrA studied in vitro using both biochemical and structural techniques.

Mobilisation of pC221 has been observed in the presence of self-transmissible plasmids. In addition to the relaxase protein MobA we have identified a crucial accessory protein, MobC, which is common to all plasmids of this family. Our current studies of the relaxase complex are directed towards understanding the roles of MobA and MobC in the specific recognition of the cognate transfer origin, oriT, and how they bring about the cleavage process.


Faculty Research and Innovation

Studentship information

Undergraduate project topics:

  • Typical laboratory projects on offer are concerned with MRSA and DNA replication; more recently students have also been working on plasmid replication in thermophilic bacteria. Projects are usually chosen by students looking to gain experience in molecular biology techniques (PCR, cloning etc.) but the precise content can usually be adjusted to suit the student's interests.

Postgraduate studentship areas:

  • Plasmid replication and transfer; maintenance of chromosomal DNA; protein:DNA and protein:protein interactions; development of novel targets for antibiotics.

See also:

Modules managed

BIOC1302 - Introductory Biochemistry: Practical Skills

Modules taught

BIOC1302 - Introductory Biochemistry: Practical Skills
BIOC1303 - Introductory Biochemistry: Problem Solving and Data Handling
BIOC2303 - Intermediate Biochemistry: Skills
BIOC3231/32/BIOL3211/MICR3212 c - ATU - DNA maintenance in pathogens
BIOL2301/03/MICR2320/BIOL3400 - BIOL/BIOC/MICR advanced skills/Skills in the Cell Biology of Human Disease
BIOL5294M - MSc Bioscience Research Project Proposal
BIOL5392M - Bioscience MSc Research Project
BMSC1213 - Basic Laboratory and Scientific Skills 2
MICR3080 - Microbiology Research Project
SPSC2203 - Exercise Biochemistry

Centre memberships:

Group Leader Dr Christopher Thomas  (Lecturer)

Replication- and conjugation-specific proteins and the maintenance of extrachromosomal DNA