| Summary: | 碩士 === 國立臺灣大學 === 植物科學研究所 === 99 === DUF28 protein family ubiquitously exists in all organisms, except Archaea; however, information on their function is very limited. Previous studies demonstrated that DUF28 is involved in Pseudomonas aeruginosa swarming motility and quorum sensing, and functions as a translational activator of COX I in mammals. Interestingly, this study revealed the existence of two DUF28 homologs in some eubacteria. The aim of this study was to investigate functions of the two E. coli DUF28 proteins, namely YeeN and YebC, particularly their function in oxidative stress responses. Sequence comparisons revealed that bacterial DUF28 proteins shared low similarity, implying these proteins may preserve conserved tertiary structure. Null mutants ΔyeeN and ΔyebC both displayed increased swarming and swimming activities, while only ΔyeeN conferred increased tolerance to paraquat. Complementation assays further confirmed functions of these two proteins in motility and paraquat tolerance. Promoter analysis demonstrated that yeeN has its own promoter that can be repressed by oxidative stress. yebC promoter functioned only later growth phase and was not regulated by the test oxidative stress treatments. Protein localization analysis showed that accumulation and stress conditions could lead to polar distribution of YeeN in cytosol, while YebC uniformly distributed in cytosol and became polar distribution in a fragmented manner only at the death growth phase. Furthermore, by investigating the putative regulatory genes that may be involved in yeeN regulation, this study showed that recA could regulate yeeN under oxidative stress treatment. relA could upregulate yeeN expression under normal condition, but may not be involved in yeeN regulation under oxidative stress. On the other hand, hns could downregulate yeeN expression in late growth phase, and may regulate yeeN in flagella biosynthesis. Taken together, these results indicate that YeeN and YebC both function in bacterial motility, while YeeN also plays an important role in oxidative stress responses. This study is the first to uncover common as well as distinct functions of two bacterial DUF28 proteins.
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