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J. Bacteriol., Mar 1996, 1289-1294, Vol 178, No. 5
DL Marykwas and HC Berg
The motor that drives the flagellar filament of Escherichia coli contains
three "switch" proteins (FliG, FliM, and FliN) that together determine the
direction of rotation. Each is required, in addition, for flagellar
assembly and for torque generation. These proteins interact in the
Saccharomyces cerevisiae two-hybrid system: FliG interacts with FliM, FliM
interacts with itself, and FliM interacts with FliN. The interaction
between FliG and FliM has been subjected to mutational analysis. FliG
(fused to the GAL4 DNA-binding domain) and FliM (fused to a GAL4
transcription activation domain) together activate transcription of a
GAL4-dependent lacZ reporter gene. DNA encoding FliG was mutagenized by
error-prone amplification with Taq polymerase, mutant fliG genes were
cloned (as DNA-binding domain-fliG gene fusions) in S. cerevisiae by gap
repair of plasmid DNA, and mutants exhibiting an interaction defect were
isolated in a two-hybrid screen. The mutations were each mapped to the
first, second, or last third of the fliG gene by multifragment cloning in
vivo and then identified by DNA sequencing. In this way, we identified 18
interaction-defective and 15 silent (non-interaction-defective) fliG
mutations. Several residues within the middle third of FliG are strongly
involved in the FliG-FliM interaction, while residues near the N or C
terminus are less important. This clustering, when compared with results of
previous studies, suggests that the FliG-FliM interaction plays a central
role in switching.
Copyright © 1996, American Society for Microbiology
A mutational analysis of the interaction between FliG and FliM, two components of the flagellar motor of Escherichia coli
Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
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