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HOME > J. Microbiol > Volume 53(12); 2015 > Article
Research Support, Non-U.S. Gov't
Characterization of cell death in Escherichia coli mediated by XseA, a large subunit of exonuclease VII
Hyeim Jung , Junwei Liang , Yuna Jung , Dongbin Lim
Journal of Microbiology 2015;53(12):820-828.
DOI: https://doi.org/10.1007/s12275-015-5304-0
Published online: December 2, 2015
School of Systems Biomedical Science, Soongsil University, Seoul 06978, Republic of KoreaSchool of Systems Biomedical Science, Soongsil University, Seoul 06978, Republic of Korea
Corresponding author:  Dongbin Lim , Tel: +82-2-820-0452, 
Received: 17 June 2015   • Revised: 6 November 2015   • Accepted: 18 November 2015
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Abstract

Exonuclease VII (ExoVII) of Escherichia coli is a single strandspecific DNA nuclease composed of two different subunits: the large subunit, XseA, and the small subunit, XseB. In this study, we found that multicopy single-stranded DNAs (msDNAs), Ec83 and Ec78, are the in vivo substrates of ExoVII; the enzyme cuts the phosphodiester bond between the fourth and fifth nucleotides from the 5′ end. We used this msDNA cleavage to assess ExoVII activity in vivo. Both subunits were required for enzyme activity. Expression of XseA without XseB caused cell death, even though no ExoVII activity was detected. The lethality caused by XseA was rescued by surplus XseB. In XseA-induced death, cells were elongated and multinucleated, and their chromosomes were fragmented and condensed; these are the morphological hallmarks of apoptotic cell death in bacteria. A putative caspase recognition sequence (FVAD) was found in XseA, and its hypothetical caspase product with 257 amino acids was as active as the intact protein in inducing cell death. We propose that under ordinary conditions, XseA protects chromosome as a component of the ExoVII enzyme, but in some conditions, the protein causes cell death; the destruction of cell is probably carried out by the amino terminal fragment derived from the cleavage of XseA by caspase-like enzyme.

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    Characterization of cell death in Escherichia coli mediated by XseA, a large subunit of exonuclease VII
    J. Microbiol. 2015;53(12):820-828.   Published online December 2, 2015
    DOI: https://doi.org/10.1007/s12275-015-5304-0
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