Colicins are considered model proteins for studying bacterial toxins. These narrow spectrum antibiotics can kill by a variety of mechanisms, e.g. by forming pores in the membranes of susceptible cells or by degrading their nucleic acids. Colicin genes are plasmid-encoded and repressed by the master regulator of the DNA damage response, LexA. Induction of several pore-forming colicin genes is also repressed by IscR, which ensures that colicin genes are switched on as a last resort in DNA damaged cells, when nutrients are depleted. Here we show that nuclease colicin genes are not controlled by IscR but that the AsnC protein, in concert with LexA, is directly responsible for uncoupling the immediate expression of the DNase colicin E8 from the main induction of the SOS response. AsnC wraps the DNA of the colicin E8 promoter into a complex nucleoprotein assembly and the architecture of this complex is altered by the presence of the amino acid L-asparagine. Thus, repression by metabolite-responsive and DNA-damage responsive regulators operates at the regulatory regions of different colicins. Hence, the response to several environmental signals have been integrated to ensure that, following DNA damage, colicin synthesis is tightly repressed and induced only in terminally damaged cells.
Vyšlo v časopise: Silencing of DNase Colicin E8 Gene Expression by a Complex Nucleoprotein Assembly Ensures Timely Colicin Induction. PLoS Genet 11(6): e32767. doi:10.1371/journal.pgen.1005354 Kategorie: Research Article prolekare.web.journal.doi_sk: https://doi.org/10.1371/journal.pgen.1005354
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