Open Access Research article

The Escherichia coli uropathogenic-specific-protein-associated immunity protein 3 (Imu3) has nucleic acid -binding activity

Miha Črnigoj, Zdravko Podlesek, Maruška Budič and Darja Žgur-Bertok*

Author Affiliations

Department of Biology, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia

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BMC Microbiology 2014, 14:16  doi:10.1186/1471-2180-14-16

Published: 28 January 2014



The Escherichia coli uropathogenic-specific protein (Usp) is a bacteriocin-like genotoxin, active against mammalian cells and associated with E. coli strains that provoke pyelonephritis, prostatitis and bacteraemia. Usp is encoded by a small pathogenicity island with three downstream small open reading frames (Imu1-3) that are believed to provide immunity to the producer. To prevent host suicide, colicins, bacteriocins of E. coli, form tight complexes with their cognate immunity proteins. Colicin – immunity protein complexes are among the strongest protein complexes known. Here, the Usp associated immunity protein 3 (Imu3) was partially characterized to gain insight into its role and mechanism of activity.


Isolation and partial characterisation of the Usp-associated immunity protein-3 (Imu3) revealed that, while Usp and Imu3 do not form a high affinity complex, Imu3 exhibits DNA and RNA binding activity. Imu3 was also shown to protect DNA against degradation by colicin E7.


Our data infer that nonspecific DNA binding of the Imu3 immunity protein, prevents suicide of E. coli producing the genotoxin Usp.

Escherichia coli; Imu3; Immunity protein; Uropathogenic-specific protein DNA/RNA binding