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Alan Leonard

Alan Leonard

Dr. Leonard’s research interests are focused on the regulatory mechanisms that control normal cell growth, particularly the cell cycle-specific assembly of protein complexes that trigger new rounds of chromosome replication.
 
      Members of his laboratory (with Dr. Juila Grimwade) have developed methods for high-resolution analysis of regulatory complexes in synchronously-dividing and non-synchronous cell populations.  Although the studies are primarily focused on bacterial cells, the technology is appropriate for all cell types.   Our goal is to understand important cellular machinery and identify new targets for antibacterial compounds.
 
     Our ongoing studies are focused on important stages in the ordered assembly of E. coli pre-replication complexes, and we established that low affinity initiator protein (DnaA)-replication origin DNA (oriC) interactions are the rate-limiting step in the initiation process. We also found that DNA bending makes these interactions switch-like. 
 
Some of the low affinity DnaA binding sites also have a 3-4 fold preference for DnaA-ATP and are positioned into two convergent,  helically-phased arrays.  Our current model suggests that DnaA bound to high affinity sites nucleates DnaA-ATP oligomers that grow progressively along the DNA, directed by the low affinity sites.   Studies are currently underway to identify the stages of orisome assembly that require DnaA oligomerization.​

Publications

  • Rozgaja, T, Grimwade, J, Iqbal, M., Czerwonka, C., Vora. M., and  Leonard, A. 2011.  Two oppositely-oriented arrays of low affinity recognition sites in oriC guide progressive binding of DnaA during E. coli pre-RC assembly.  Mol. Microbiol.,  82: 475-488.
  • Leonard, A. and Grimwade, J. 2011.  Regulation of DnaA assembly and activity: taking directions from the genome.  Annual Review of Microbiology. 65:19-35.
  • Leonard, A.C., and Grimwade, J.E 2010.  Regulating DnaA complex assembly: it's time to fill the gaps, Curr. Opin. Microbiol., 13:766-772.
  • Leonard, A.C., and Grimwade, J.E. 2010. “Chromosome replication and  segregation”.  In: Encyclopedia of Microbiology, 3d edition, .M. Schaechter, ed. pp. 493-506 Oxford: Elsevier 
  • Leonard, A. C., and Grimwade, J.E.  2010. Chapter 4.4.1, Initiation of DNA Replication. In A. Böck, R. Curtiss III, J. B. Kaper, P. D. Karp, F. C.  Neidhardt, T. Nyström, J. M. Slauch, C.L. Squires, and D. Ussery (ed.), EcoSal—Escherichia coli and Salmonella: Cellular and Molecular biology. http://www.ecosal.org. ASM Press, Washington, DC. doi: 10.1128/ecosal.4.4.1
  • Miller, D.T., Grimwade, J.E., Betteridge, T., Rozgaja, T., Torgue, J.J., and Leonard, A.C. 2009. Bacterial origin recognition complexes direct assembly of higher-order DnaA oligomeric structures. Proc. Natl. Acad. Sci. (USA). 106:18479-18484.
  • Leonard, A.C. and Grimwade, J.E.  2009. Initiating chromosome replication in E. coli: it makes sense to recycle.  Genes and Development. 23:1145-50.
  • Grimwade, J.E., Torgue, J.J., McGarry, K.C., Rozgaja, T., Enloe, S.T., and Leonard, A.C. 2007. Mutational analysis reveals Escherichia coli oriC interacts with both DnaA-ATP and DnaA-ADP during pre-RC assembly. Mol. Microbiol.,66:428-39.
  • Nievera, C., Torgue, J., Grimwade, J.E., and A.C. Leonard. 2006. SeqA blocking of DnaA-oriC interactions ensures staged assembly of the E. coli pre-RC. Molecular Cell 24: 581-592.
  • Leonard, A.C. and J.E. Grimwade. 2005. Building a bacterial orisome: emergence of new regulatory features for replication origin unwinding. Mol Microbiol. 55: 978-985.
  • McGarry, K.C., V.T. Ryan, J.E. Grimwade and A.C. Leonard. 2004. Two discriminatory binding sites in the Escherichia coli replication origin are required for DNA strand opening by initiator DnaAATP. Proc. Natl. Acad. Sci (USA). 101: 2811-2816.
  • Ryan, V.T., J.E. Grimwade, J.E. Camara, E. Crooke and A.C. Leonard. 2004. Escherichia coli prereplication complex assembly is regulated by dynamic interplay among Fis, IHF and DnaA. Mol. Microbiol. 51:1347-1359.
  • Ryan, V.T., J.E. Grimwade, C.J. Nievera and A.C. Leonard. 2002. IHFand HU stimulate assembly of pre-replication complexes at Escherichia coli by two different mechanisms. Mol. Microbiol. 46: 113-124.
  • Grimwade, J.E., V.T. Ryan and A.C. Leonard. 2000. IHF redistributes bound initiator protein, DnaA, on supercoiled oriC of Escherichia coli. Mol. Microbiol. 35: 835-844. 
  • Cassler, M.R., J..E. Grimwade and A.C. Leonard. 1995. Cell cycle-specific changes in nucleoprotein complexes at a chromosomal replication origin. EMBO J. 14: 5833-5841. 
  • Leonard, A.C. and C.E. Helmstetter. 1986. Cell-Cycle Specific Replication of Escherichia coli minichromosomes. Proc. Natl. Acad. Sci. (USA). 83: 5101-5105.

Article of the month

• Murray et.al. The bacterial Dana-trio replication origin element specifies single-stranded DNA initiator binding Nature, Vol. 536, No. 910. ( 2016), pp. 488.