| Summary: | <i>Agrobacterium tumefaciens</i> is a pathogen of various plants which transfers its own DNA (T-DNA) to the host plants. It is used for producing genetically modified plants with this ability. To control T-DNA transfer to the right place, toxin-antitoxin (TA) systems of <i>A. tumefaciens</i> were used to control the target site of transfer without any unintentional targeting. Here, we describe a toxin-antitoxin system, <i>Atu0939 (mazE-at)</i> and <i>Atu0940 (mazF-at)</i>, in the chromosome of <i>Agrobacterium tumefaciens</i>. The toxin in the TA system has 33.3% identity and 45.5% similarity with MazF in <i>Escherichia coli</i>. The expression of MazF-at caused cell growth inhibition, while cells with MazF-at co-expressed with MazE-at grew normally. In vivo and in vitro assays revealed that MazF-at inhibited protein synthesis by decreasing the cellular mRNA stability. Moreover, the catalytic residue of MazF-at was determined to be the 24th glutamic acid using site-directed mutagenesis. From the results, we concluded that MazF-at is a type II toxin-antitoxin system and a ribosome-independent endoribonuclease. Here, we characterized a TA system in <i>A. tumefaciens</i> whose understanding might help to find its physiological function and to develop further applications.
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