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Journal of Bacteriology, November 1999, p. 6898-6906, Vol. 181, No. 22
Bioengineering Centre, Russian
Academy of Sciences, Moscow, 117312 Russia,1 and
Laboratoire de Microbiologie et Génétique
Moléculaire, 31062 Toulouse, France2
Received 26 July 1999/Accepted 1 September 1999
A locus close to one end of the linear N15 prophage closely
resembles the sop operon which governs partition of the F
plasmid; the promoter region contains similar operator sites, and the
two putative gene products have extensive amino acid identity with the
SopA and -B proteins of F. Our aim was to ascertain whether the N15
sop homologue functions in partition, to identify the centromere site, and to examine possible interchangeability of function
with the F Sop system. When expressed at a moderate level, N15 SopA and
-B proteins partly stabilize mini-F which lacks its own sop
operon but retains the sopC centromere. The stabilization does not depend on increased copy number. Likewise, an N15 mutant with
most of its sop operon deleted is partly stabilized by F Sop proteins and fully stabilized by its own. Four inverted repeat sequences similar to those of sopC were located in N15.
They are distant from the sop operon and from each other.
Two of these were shown to stabilize a mini-F sop deletion
mutant when N15 Sop proteins were provided. Provision of the SopA
homologue to plasmids with a sopA deletion resulted in
further destabilization of the plasmid. The N15 Sop proteins exert
effective, but incomplete, repression at the F sop
promoter. We conclude that the N15 sop locus determines
stable inheritance of the prophage by using dispersed centromere sites.
The SopB-centromere and SopA-operator interactions show partial
functional overlap between N15 and F. SopA of each plasmid appears to
interact with SopB of the other, but in a way that is detrimental to
plasmid maintenance.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Partition of the Linear Plasmid N15: Interactions
of N15 Partition Functions with the sop Locus of the F
Plasmid
*
Corresponding author. Mailing address: Laboratoire de
Microbiologie et Génétique Moléculaire, 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.
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