Journal of Bacteriology, February 2001, p. 1413-1422, Vol. 183, No. 4
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.4.1413-1422.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Department of Microbiology and Molecular Genetics, University of Texas-Houston Medical School, Houston, Texas 77030
Received 5 July 2000/Accepted 15 November 2000
We previously presented evidence that replicating but unsegregated nucleoids, along with the Min system, act as topological inhibitors to restrict assembly of the FtsZ ring (Z ring) to discrete sites in the cell. To test if nonreplicating nucleoids have similar exclusion effects, we examined Z rings in dnaA (temperature sensitive) mutants. Z rings were excluded from centrally localized nucleoids and were often observed at nucleoid edges. Cells with nonreplicating nucleoids formed filaments, some of which contained large nucleoid-free areas in which Z rings were positioned at regular intervals. Because MinE may protect FtsZ from the action of the MinC inhibitor in these nucleoid-free zones, we examined the localization of a MinE-green fluorescent protein (GFP) fusion with respect to Z rings and nucleoids. Like Z rings, MinE-GFP appeared to localize independently of nucleoid position, forming rings at regular intervals in nucleoid-free regions. Unlike FtsZ, however, MinE-GFP often localized on top of nucleoids, replicating or not, suggesting that MinE is relatively insensitive to the nucleoid inhibition effect. These data suggest that both replicating and nonreplicating nucleoids are capable of topologically excluding Z rings but not MinE.
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