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The supercoiling sensitivity of a bacterial tRNA promoter parallels its responsiveness to stringent control
Author(s) -
FigueroaBossi Nara,
Guérin Martine,
Rahmouni Rachid,
Leng Marc,
Bossi Lionello
Publication year - 1998
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/17.8.2359
Subject(s) - dna supercoil , biology , stringent response , operon , promoter , transcription (linguistics) , rna polymerase , microbiology and biotechnology , dna gyrase , dna , mutant , genetics , rna , gene , gene expression , escherichia coli , dna replication , linguistics , philosophy
In Salmonella typhimurium , expression of the hisR locus, a tRNA operon, decreases upon inhibiting DNA gyrase. Here, the hisR promoter dependence on negative DNA supercoiling was examined in vivo and in vitro . Mutant analysis showed the sequence determinants of this dependence to lie in the region between the −10 box and the transcription start site. As with most promoters subject to stringent control, this portion of the hisR promoter is C–G‐rich. Replacing a C/G bp with T/A at position −7 partially relieves the supercoiling response while changing the sequence between −5 and +1 (‐G‐) for ‐GTTAA‐ abolishes the response in vitro and in vivo . The relief of the supercoiling dependence closely correlates with increased promoter susceptibility to melting in vivo and a lesser requirement for initiating nucleotides in the formation of stable initiation complexes in vitro . Studies in isoleucine‐starved cells showed that such sequence changes mitigate and abolish the hisR promoter response to stringent control, respectively. The data presented suggest that the hisR promoter's sensitivity to stringent regulation arises from the same physical property that confers supercoiling sensitivity, i.e. resistance to melting. We propose that the stringent control mechanism acts by hampering the ability of RNA polymerase to melt the DNA helix.