Major Research Areas
Immunology

In close collaboration with the Shuman laboratory of the Molecular Biology program here at MSKCC, we are investigating a family of ATP dependent DNA ligases present in mycobacteria.  In addition to LigA, the essential NAD dependent DNA ligase present in all bacteria, the  Myocbacterium smegmatis and Mycobacterium tuberculosis genomes both encode multiple  ATP dependent DNA ligases. Although some bacterial genomes were known to encode an additional ATP dependent ligase, the duplication of multiple such enzymes in mycobacterial genomes is unique. Using a combined biochemical, genetic, and physiologic approaches, we are actively investigating the role of these ATP dependent DNA ligases in mycobacterial DNA repair and pathogenesis. 

We have shown that both M. smegmatis and M. tuberculosis express an active pathway of Non Homologous End Joining (NHEJ) for repair of double strand DNA breaks (DSB).  While NHEJ is a well studied pathway of DSB repair in eukaryotic cells, homologous recombination was previously thought to be the sole pathway of DSB repair in prokaryotes.  Using M. tuberculosis and M. smegmatis null mutants in each ATP dependent ligase and Ku, we have shown that mycobacterial NHEJ requires LigD and Ku and these two protein interact physically (see figure).  In addition, the  LigD protein has DNA polymerase activity which acts to remodel DNA ends during end-joining, resulting in highly mutagenic NHEJ.  For more details of this novel DNA repair pathway, please see publications associated with this project and the link to the Shuman laboratory.

Figure 1
Ku interacts physically with LigD and is required for mycobacterial NHEJ
from Gong et al, Nat Struct Mol Biol 2005 Apr;12(4):304-12

The experimental questions we are addressing are:

  1. What is the physiologic and pathogenetic role of NHEJ and does mycobacterial NHEJ defend against host inflicted DNA damage during infection
  2. What are the other  components of the mycobacterial NHEJ machinery.
  3. Does mycobacterial NHEJ mediate sequence diversity through mutagenic repair of double strand breaks.


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