Abstract
In previous studies we demonstrated that mutations in the genes cysB, cysE, and cls (nov) affect resistance of Escherichia coli to novobiocin (J. Rakonjac, M. Milic, and D. J. Savic, Mol. Gen. Genet. 228:307-311, 1991; R. Ivanisevic, M. Milic, D. Ajdic, J. Rakonjac, and D. J. Savic, J. Bacteriol. 177:1766-1771, 1995). In this work we expand this list with mutations in rpoN (the gene for RNA polymerase subunit sigma54) and the tRNA synthetase genes alaS, argS, ileS, and leuS. Similarly to resistance to the penicillin antibiotic mecillinam, resistance to novobiocin of tRNA synthetase mutants appears to depend upon the RelA-mediated stringent response. However, at this point the overlapping pathways of mecillinam and novobiocin resistance diverge. Under conditions of stringent response induction, either by the presence of tRNA synthetase mutations or by constitutive production of RelA protein, inactivation of the cls gene diminishes resistance to novobiocin but not to mecillinam.
Highlights
The coumarin antibiotics novobiocin, coumermycin A1, and chlorobiocin inhibit DNA supercoiling reactions by blocking the B subunit (GyrB) of DNA gyrase [4, 5]
To address the question of how the activity of cls correlates with increased resistance of aminoacyl-tRNA synthetase mutants to both novobiocin and mecillinam, we introduced by P1vir transduction the inactivated cls allele into ileS80, alaS21, and argS201 recipients
We lengthen the list of gyrBunrelated genes that affect E. coli resistance to novobiocin
Summary
C600 GC2553 GC3743 (KL231) GC3802 GC3814 SY433 SY434 SY437 SY438 SY439 SY440 SY444 SY456 SY468 SY500 SY501 SY502 SY503 SY504 SY505 SY506 SY508 SY510 SY511 XL1-Blue Plasmids pSYC988 pSM11. Vinella This work This work This work This work This work This work Laboratory collection Laboratory collection This work This work This work This work This work This work This work This work This work This work This work 2 8 15 by exerting a polar effect on expression of the downstream lsp gene That this is not the case was demonstrated by complementation experiments with derivatives of plasmid pMT521 (ileSϩ lspϩ). Introduction of plasmid pSYC988, which carries the intact ileS allele but a partially mutated lsp gene (30% of the activity of the wild-type product [8]), into both ileS mutants resulted in (full) complementation of ile auxotrophy and resistance to novobiocin (Fig. 1). These results confirm our original presumption that the wild-type allele of the ileS gene alone is sufficient for effective complementation of the dual phenotype of isoleucine auxotrophy and increased resistance to novobiocin in both ile mutants
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