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Journal of Bacteriology, May 2008, p. 3538-3545, Vol. 190, No. 10
0021-9193/08/$08.00+0     doi:10.1128/JB.01993-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Extended Function of Plasmid Partition Genes: the Sop System of Linear Phage-Plasmid N15 Facilitates Late Gene Expression{triangledown}

Nikolai V. Ravin,1 Jérôme Rech,2 and David Lane2*

Centre Bioengineering, Russian Academy of Sciences, 7-1 Prosp. 60 let Oktiabria, Moscow, 117312 Russia,1 Laboratoire de Microbiologie et Génétique Moléculaires, CNRS UMR5100, Campus Paul Sabatier, 118 route de Narbonne, 31062 Toulouse, France2

Received 21 December 2007/ Accepted 10 March 2008

The mitotic stability of the linear plasmid-prophage N15 of Escherichia coli depends on a partition system closely related to that of the F plasmid SopABC. The two Sop systems are distinguished mainly by the arrangement of their centromeric SopB-binding sites, clustered in F (sopC) and dispersed in N15 (IR1 to IR4). Because two of the N15 inverted repeat (IR) sites are located close to elements presumed (by analogy with phage {lambda}) to regulate late gene expression during the lytic growth of N15, we asked whether Sop partition functions play a role in this process. In N15, a putative Q antiterminator gene is located 6 kb upstream of the probable major late promoter and two intrinsic terminator-like sequences, in contrast to {lambda}, where the Q gene is adjacent to the late promoter. Northern hybridization and lacZ reporter activity confirmed the identity of the N15 late promoter (p52), demonstrated antiterminator activity of the Q analogue, and located terminator sequences between p52 and the first open reading frame. Following prophage induction, N15 mutated in IR2 (downstream from gene Q) or IR3 (upstream of p52) showed a pronounced delay in lysis relative to that for wild-type N15. Expression of ir3–-p52::lacZ during N15 wild-type lytic growth was strongly reduced relative to the equivalent ir3+ fusion. The provision of Q protein and the IR2 and SopAB proteins in trans to ir3+-p52::lacZ increased expression beyond that seen in the absence of any one of these factors. These results indicate that the N15 Sop system has a dual role: partition and regulation of late gene transcription during lytic growth.

* Corresponding author. Mailing address: Laboratoire de Microbiologie et Génétique Moléculaires, CNRS UMR5100, Campus Paul Sabatier, 118 route de Narbonne, 31062 Toulouse, France. Phone: 33 5 61 33 59 68. Fax: 33 5 61 33 58 86. E-mail: dave{at}ibcg.biotoul.fr

{triangledown} Published ahead of print on 21 March 2008.

Journal of Bacteriology, May 2008, p. 3538-3545, Vol. 190, No. 10
0021-9193/08/$08.00+0     doi:10.1128/JB.01993-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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