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Journal of Bacteriology, September 2000, p. 5153-5166, Vol. 182, No. 18
Department of Molecular Biology and
Microbiology, Case Western Reserve University School of Medicine,
Cleveland, Ohio 44106-4960
Received 28 March 2000/Accepted 23 June 2000
FtsZ and ZipA are essential components of the septal ring
apparatus, which mediates cell division in Escherichia
coli. FtsZ is a cytoplasmic tubulin-like GTPase that forms
protofilament-like homopolymers in vitro. In the cell, the protein
assembles into a ring structure at the prospective division site early
in the division cycle, and this marks the first recognized event in the assembly of the septal ring. ZipA is an inner membrane protein which is
recruited to the nascent septal ring at a very early stage through a
direct interaction with FtsZ. Using affinity blotting and protein
localization techniques, we have determined which domain on each
protein is both sufficient and required for the interaction between the
two proteins in vitro as well as in vivo. The results show that ZipA
binds to residues confined to the 20 C-terminal amino acids of FtsZ.
The FtsZ binding (FZB) domain of ZipA is significantly larger and
encompasses the C-terminal 143 residues of ZipA. Significantly, we find
that the FZB domain of ZipA is also required and sufficient to induce
dramatic bundling of FtsZ protofilaments in vitro. Consistent with the
notion that the ability to bind and bundle FtsZ polymers is essential
to the function of ZipA, we find that ZipA derivatives lacking an
intact FZB domain fail to support cell division in cells depleted for the native protein. Interestingly, ZipA derivatives which do contain an
intact FZB domain but which lack the N-terminal membrane anchor or in
which this anchor is replaced with the heterologous anchor of the DjlA
protein also fail to rescue ZipA
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
ZipA-Induced Bundling of FtsZ Polymers Mediated by
an Interaction between C-Terminal Domains
cells. Thus, in addition
to the C-terminal FZB domain, the N-terminal domain of ZipA is required
for ZipA function. Furthermore, the essential properties of the N
domain may be more specific than merely acting as a membrane anchor.
*
Corresponding author. Mailing address: Department of
Molecular Biology and Microbiology, Case Western Reserve University
School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106-4960. Phone: (216) 368-1697. Fax: (216) 368-3055. E-mail:
pad5{at}po.cwru.edu.
This study is dedicated to the memory of Joe Polak, whose expertise
and cheerfulness are sorely missed.
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