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Journal of Bacteriology, July 2006, p. 4681-4689, Vol. 188, No. 13
0021-9193/06/$08.00+0     doi:10.1128/JB.00332-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Plasticity of the P_junc Promoter of ISEc11, a New Insertion Sequence of the IS1111 Family

Gianni Prosseda,^1, Maria Carmela Latella,^1, Mariassunta Casalino,² Mauro Nicoletti,³ Stefano Michienzi,² and Bianca Colonna^1*

Dipartimento Biologia Cellulare e dello Sviluppo, Università La Sapienza, 00185 Rome, Italy,¹ Dipartimento Biologia, Università Roma 3, 00146 Rome, Italy,² Dipartimento Scienze Biomediche, Università G. D'Annunzio, 66100 Chieti, Italy³

Received 7 March 2006/ Accepted 10 April 2006

We describe identification and functional characterization of ISEc11, a new insertion sequence that is widespread in enteroinvasive E. coli (EIEC), in which it is always present on the virulence plasmid (pINV) and very frequently also present on the chromosome. ISEc11 is flanked by subterminal 13-bp inverted repeats (IRs) and is bounded by 3-bp terminal sequences, and it transposes with target specificity without generating duplication of the target site. ISEc11 is characterized by an atypical transposase containing the DEDD motif of the Piv/MooV family of DNA recombinases, and it is closely related to the IS1111 family. Transposition occurs by formation of minicircles through joining of the abutted ends and results in assembly of a junction promoter (P_juncC) containing a –10 box in the interstitial sequence and a –35 box upstream of the right IR. A natural variant of ISEc11 (ISEc11p), found on EIEC pINV plasmids, contains a perfect duplication of the outermost 39 bp of the right end. Upon circularization, ISEc11p forms a junction promoter (P_juncP) which, despite carrying –10 and –35 boxes identical to those of P_juncC, exhibits 30-fold-greater strength in vivo. The discovery of only one starting point in primer extension experiments rules out the possibility that there are alternative promoter sites within the 39-bp duplication. Analysis of in vitro-generated transcripts confirmed that at limiting RNA polymerase concentrations, the activity of P_juncP is 20-fold higher than the activity of P_juncC. These observations suggest that the 39-bp duplication might host cis-acting elements that facilitate the binding of RNA polymerase to the promoter.

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* Corresponding author. Mailing address: Dipartimento di Biologia Cellulare e dello Sviluppo, Via dei Sardi 70, 00185 Roma, Italy. Phone: (39 6) 49917580. Fax: (39 6) 49917594. E-mail: bianca.colonna{at}uniroma1.it.

G.P. and M.C.L. contributed equally to this work.

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Journal of Bacteriology, July 2006, p. 4681-4689, Vol. 188, No. 13
0021-9193/06/$08.00+0     doi:10.1128/JB.00332-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Tetu, S. G., Holmes, A. J. (2008). A Family of Insertion Sequences That Impacts Integrons by Specific Targeting of Gene Cassette Recombination Sites, the IS1111-attC Group. J. Bacteriol. 190: 4959-4970 [Abstract] [Full Text]