Steven M. Theg

Steven Theg

Position Title

Department of Plant Biology, College of Biological Sciences

2225 Life Sciences Addition

Research Interests

Protein transport

Protein translocation across biological membranes, with a focus on chloroplast membranes. Mechanism of multimeric protein complex assembly. Chloroplast bioenergetics.

The current objectives of the research in the Theg lab are to understand the events surrounding the transport of proteins across biological membranes and their assembly into larger multimeric complexes. Most of the laboratory's efforts focus on protein trafficking and assembly in chloroplasts isolated from higher plants (often peas, but also Arabidopsis and the moss Physcomitrella patens).

These organelles represent an excellent model system in which to study cellular protein targeting as they are easily separated from other organelles, and retain a high level of metabolic activity after isolation. In addition, they contain a level of structural complexity that requires additional sorting of proteins within the organelle. In these sorting reactions, chloroplasts utilize different protein targeting paradigms which are individually used by other organelles. Consequently, lessons learned from the study of protein targeting to and within chloroplasts can, in principle, be applied to a number of other polypeptide translocating systems.

We have also made recent forrays into the mechanism of thylakoid division and the biochemistry of stromule formation.

Grad Group Affiliations

  • Biochemistry, Molecular, Cellular and Developmental Biology
  • Biophysics
  • Plant Biology

Specialties / Focus

  • Biochemistry
  • Biochemistry and Molecular Recognition
  • Cell and Developmental Biology
  • Cell Biology
  • Molecular Biology, Biochemistry and Genomics
  • Molecular Genetics
  • Organelle and Membrane Biology
  • Plant Molecular Biology
  • Structural Biology, Membranes and Macromolecular Assembly


  • Bis 102 Structure and Function of Biomolecules, Fall
  • Bis 105 Biomolecules and Metabolism, Fall, Spring
  • MCB 120L Biochemistry Laboratory, Fall

Professional Societies

  • American Society of Plant Physiologists


  • 1977 BS Biology Boston College
  • 1981 PhD Molecular Biophysics Florida State University


Yang, H., Pu, X., Wang, L,. Liu, L. and Theg, S.M. (2017) A new fluorescence-based method to monitor the pH in the thylakoid lumen using GFP variants. Biochem Biophys Res Commun. 486: 1-5. doi: 10.1016/j.bbrc.2016.12.032.

Ho, J. and Theg, S.M. (2015) The Formation of Stromules In Vitro from Chloroplasts Isolated from Nicotiana Benthamiana. PLOS ONE doi:10.1371/journal.pone.0146489 

Wang, X, Wei, Y., Shi, L-X., Ma, X and Theg, S.M. (2015) New Isoforms and Assembly of Glutamine Synthetase in the Leaf of Wheat (Triticum aestivum L.).  J. Exp. Bot. 66:6827-6834.  doi: 10.1093/jxb/erv388

Liu, L., McNielage, R.T., Shi, L.-X. and Theg, S.M. (2014) ATP requirement for chloroplast protein import is set by the Km for ATP hydrolysis of the stromal Hsp70 in Physcomitrella patens.  Plant Cell 26: 1246-1255.  doi: 10.1105/tpc.113.121822

Bricker, T.M., Bell, A.J., Tran, L. Frankel, L.K. and Theg, S.M. (2013) Photoheterotrophic growth of Physcomitrella patens.  Planta 293: 605-613.  doi:  10.1007/s00425-013-2000-3

Shi, L-X. and Theg, S.M. (2013) The energetic cost of protein import across the envelope membranes of chloroplasts.  Proc. Natl. Acad. Sci. USA, 110:930-935.

Shi, L-X. and Theg, S.M. (2013) The chloroplast protein import system: From algae to trees.  Biochim. Biophys. Acta  1833:314–331.

Lo, S.M. and Theg, S.M. (2012) Role of Vesicle-Inducing Protein in Plastids 1 in cpTat Transport at the Thylakoid. The Plant J. 71:656-668.

Shi, L-X. and Theg, S.M. (2011) The motors of protein import into chloroplasts. Plant Signaling & Behavior 6:1397-1401.

Theg, S.M. and Tom, C. (2011) Measurement of the ΔpH and electric field developed across Arabidopsis thylakoids in the light. Methods Mol. Biol. 775:327-357.

Shi, L-X. and Theg, S.M. (2010) A Stromal Hsp70 System Functions in Protein Import into Chloroplasts in the Moss Physcomitrella patens. The Plant Cell 22:1-16.

Lo, S.M. and Theg, S.M.(2010) Protein Targeting Across and Into Chloroplast Membranes. Methods Mol. Biol. 684:139-157.

Theg, S.M. (2010) Measurement of the Energetics of Protein Transport across the Chloroplast Thylakoid Membrane. Methods Mol. Biol. 619:323-337.