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J. Bacteriol. doi:10.1128/JB.01528-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Processing of as-48ABC RNA in AS-48 enterocin production by Enterococcus faecalis

Dpto de Microbiología, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain; Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain

^* To whom correspondence should be addressed. Email: mmaqueda{at}ugr.es.

	Abstract

Enterocin AS-48 production and immunity characters are encoded by ten genes (as-48ABCC₁DD₁EFGH) of the pMB2 plasmid from the Enterococcus faecalis S-48 strain. Among these, as-48A, encoding the AS-48 peptide, and the as-48BC genes, constitute a cluster required for AS-48 biogenesis and full immunity. In this study the levels of expression of this cluster have been altered by insertion and site directed mutagenesis, as well as by expression coupled to trans complementation. Phenotypic studies of the mutants have indicated co-transcription of the three genes, and revealed that inactivation of as-48B prevents the AS-48 production, thus confirming its essentiality in AS-48 biogenesis. These studies have also supported the involvement of as-48C in enterocin immunity. In addition, they established that the intergenic region between the as-48A and as-48B genes is decisive for AS-48 expression, since a 3-base-pair substitution, which should disrupt a potential 47 nt complex secondary structure, resulted in a hypo-producing phenotype. Transcriptional analysis of the E. faecalis wild-type and mutant strains supports that the as-48ABC genes are transcribed from the P_A promoter located upstream of as-48A. Moreover, analysis and bioinformatic predictions of RNA folding indicate that the as-48ABC mRNA is processed at the secondary structure located between as-48A and as-48B. Thus, synthesis of the AS-48 peptide appears to be controlled at the post-transcriptional level, and is uncoupled from as-48BC translation. This is a mechanism of genetic regulation not previously described for regulation of bacteriocin expression in enterococci.

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