Intracellular microcin J25 represses the activity of the structural gene promoter

ARIAS, VJ; LACHENICHT, JA; SALOMÓN, RA

Ciudad Autónoma de Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

Sociedades de Biociencias

Microcin J25 (MccJ25) is a 21-amino-acid, plasmid-encoded antibacterial peptide produced by Escherichia coli. Its target of action is bacterial RNA polymerase. MccJ25 synthesis requires four genes and is induced in stationary phase. The structural gen mcjA encodes a 58-residue precursor, which is posttranslationally modified by the mcjB and mcjC gene products. The mcjD gene specifies an exporter and also provides immunity against the peptide. It was observed that microcin production is similar when the mcjA gene is cloned in a low- or a high-copy number plasmid. A possible explanation could be that the peptide represses its own production when it accumulates above certain threshold. To test this hypothesis, we cloned a DNA fragment containing the mcjA promoter in the promoter probe plasmid pRS415, generating a transcriptional fusion with the lacZ reporter gene. The recombinant plasmid was introduced in a strain previously transformed with a MccJ25-producing plasmid. β-galactosidase activity was measured during exponential and stationary phases. Levels of β-galactosidase were tenfold lower in the strain producing microcin than in the non-producing control carrying a mcjA gene inactivated by Tn5 insertion. These results support the notion of a negative autoregulation of MccJ25 synthesis. We are investigating whether this effect of MccJ25 is direct, or mediated through its action on RNA polymerase.