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Journal of Bacteriology, August 2001, p. 4543-4550, Vol. 183, No. 15
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.15.4543-4550.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Escherichia coli RNA Polymerase Is the Target of the Cyclopeptide Antibiotic Microcin J25

Mónica A. Delgado, María R. Rintoul, Ricardo N. Farías, and Raúl A. Salomón*

Departamento de Bioquímica de la Nutrición, Instituto Superior de Investigaciones Biológicas (Consejo Nacional de Investigaciones Cientificas y Técnicas-Universidad Nacional de Tucumán), and Instituto de Química Biológica "Dr. Bernabé Bloj," Chacabuco 461, 4000 San Miguel de Tucumán, Tucumán, Argentina

Received 30 April 2001/Accepted 10 May 2001

Escherichia coli microcin J25 (MccJ25) is a plasmid-encoded, cyclic peptide antibiotic consisting of 21 unmodified amino acid residues. It is primarily active on gram-negative bacteria related to the producer strain, inducing cell filamentation in an SOS-independent way. A mutation causing resistance to MccJ25 was isolated. Genetic analysis indicated that it resided in the rpoC gene, encoding the beta ' subunit of RNA polymerase, at 90 min on the E. coli genetic map. The mutation was genetically crossed on to a plasmid containing the wild-type rpoC gene. The presence of the recombinant plasmid conferred complete resistance to otherwise sensitive strains. Nucleotide sequencing of the plasmid-borne, mutant rpoC gene revealed a ACC (Thr)-to-ATC (Ile) change at codon 931, within homology block G, an evolutionarily conserved region in the large subunits of all RNA polymerases. MccJ25 decreased RNA synthesis both in vivo and in vitro. These results point to the RNA polymerase as the target of microcin action. We favor the possibility that the filamentous phenotype induced by MccJ25 results from impaired transcription of genes coding for cell division proteins. As far as we know, MccJ25 is the first peptide antibiotic shown to affect RNA polymerase.

* Corresponding author. Mailing address: Departamento de Bioquímica de la Nutrición, INSIBIO, Chacabuco 461, 4000 San Miguel de Tucumán, Argentina. Phone: (54) (381) 4248921. Fax: (54) (381) 4248025. E-mail: salomon{at}unt.edu.ar.

Journal of Bacteriology, August 2001, p. 4543-4550, Vol. 183, No. 15
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.15.4543-4550.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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