Posttranscriptional repression of the cel gene of the CoIE7 operon by the RNA-binding protein CsrA of Escherichia coli (Nucleic Acids Res, 2010, 38:3936-3951)

報告日期: 2011/03/01
報告時間: 15:10/16:00
報告學生: 高正彥 (英文報告)
講評老師: 何漣漪

Full Text:

Posttranscriptional repression of the cel gene of the ColE7 operon by the RNA-binding protein CsrA of Escherichia coli
Tsung-Yeh Yang, Yun-Min Sung, Guang-Sheng Lei, Tony Romeo
and Kin-Fu Chak
Nucleic Acids Research (2010) 38 (12), 3936-3951
Speaker: Cheng-Yen Kao                       Date: 2011/03/01 15:10 -16:00
Commentator: Dr. Lien-I Hor 
     Carbon storage regulator (CsrA) is a RNA binding protein that acts as a global regulator to affect the virulence factors expression, biofilm formation and bacterial motility. However, the molecular mechanisms by which environmental stimuli control the Csr global regulator system in E. coli remain unclear. In this study, the authors show that CsrA represses the lysis gene (cel) expression of the ColE7 operon from an extrachromosomal element. At first, the authors analyzed the 5’ leader region of cel mRNA and found two potential CsrA binding sites. The western blotting analysis revealed that the csrA mutant strain expressed higher lysis protein as compared to wild-type strain after mitomycin C (MMC)induction. Gel shift assays were performed in the presence or absence of unlabelled competitor RNA, and the results show that CsrA binds directly and specifically to cel mRNA. Site-directed mutagenesis of putative CsrA binding sites on CsrA-cel RNA interaction also abolished the CsrA binding activity. The authors examined the steady-state level of cel mRNA after MMC induction to determine whether the elevated protein levels in the csrA mutant are due to an increase in cel mRNA level, and the results revealed that CsrA-dependent repression of cel occurs mainly at translational level. Finally, the expression of sRNA, CsrB and CsrC, which bind to and antagonize CsrA, were dramatically reduced upon induction of the SOS response. In conclusion, during SOS response, more activated CsrA is available to negatively regulate translation of the cel mRNA.
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