J. Bacteriol., Nov 1996, 6116-6122, Vol 178, No. 21
Copyright © 1996, American Society for Microbiology

Extragenic suppression of motA missense mutations of Escherichia coli

AG Garza, PA Bronstein, PA Valdez, LW Harris-Haller and MD Manson
Department of Biology, Texas A&M University, College Station 77843- 3258, USA.

The MotA and MotB proteins are thought to comprise elements of the stator component of the flagellar motor of Escherichia coli. In an effort to understand interactions among proteins within the motor, we attempted to identify extragenic suppressors of 31 dominant, plasmid- borne alleles of motA. Strains containing these mutations were either nonmotile or had severely impaired motility. Four of the mutants yielded extragenic suppressors mapping to the FlaII or FlaIIIB regions of the chromosome. Two types of suppression were observed. Suppression of one type (class I) probably results from increased expression of the chromosomal motB gene due to relief of polarity. Class I suppressors were partial deletions of Mu insertion sequences in the disrupted chromosomal motA gene. Class I suppression was mimicked by expressing the wild-type MotB protein from a second, compatible plasmid. Suppression of the other type (class II) was weaker, and it was not mimicked by overproduction of wild-type MotB protein. Class II suppressors were point mutations in the chromosomal motB or fliG genes. Among 14 independent class II suppressors characterized by DNA sequencing, we identified six different amino acid substitutions in MotB and one substitution in FliG. A number of the strongest class II suppressors had alterations of residues 136 to 138 of MotB. This particular region within the large, C-terminal periplasmic domain of MotB has previously not been associated with a specific function. We suggest that residues 136 to 138 of MotB may interact directly with the periplasmic face of MotA or help position the N-terminal membrane- spanning helix of MotB properly to interact with the membrane-spanning helices of the MotA proton channel.

This article has been cited by other articles:

• Goemaere, E. L., Devert, A., Lloubes, R., Cascales, E. (2007). Movements of the TolR C-terminal Domain Depend on TolQR Ionizable Key Residues and Regulate Activity of the Tol Complex. J. Biol. Chem. 282: 17749-17757 [Abstract] [Full Text]  
• Van Way, S. M., Millas, S. G., Lee, A. H., Manson, M. D. (2004). Rusty, Jammed, and Well-Oiled Hinges: Mutations Affecting the Interdomain Region of FliG, a Rotor Element of the Escherichia coli Flagellar Motor. J. Bacteriol. 186: 3173-3181 [Abstract] [Full Text]  
• McClain, J., Rollo, D. R., Rushing, B. G., Bauer, C. E. (2002). Rhodospirillum centenum Utilizes Separate Motor and Switch Components To Control Lateral and Polar Flagellum Rotation. J. Bacteriol. 184: 2429-2438 [Abstract] [Full Text]  
• Kojima, S., Shoji, T., Asai, Y., Kawagishi, I., Homma, M. (2000). A Slow-Motility Phenotype Caused by Substitutions at Residue Asp31 in the PomA Channel Component of a Sodium-Driven Flagellar Motor. J. Bacteriol. 182: 3314-3318 [Abstract] [Full Text]  
• Thomas, D. R., Morgan, D. G., DeRosier, D. J. (1999). Rotational symmetry of the C ring and a mechanism for the flagellar rotary motor. Proc. Natl. Acad. Sci. USA 96: 10134-10139 [Abstract] [Full Text]  
• Zhou, J., Sharp, L. L., Tang, H. L., Lloyd, S. A., Billings, S., Braun, T. F., Blair, D. F. (1998). Function of Protonatable Residues in the Flagellar Motor of Escherichia coli: a Critical Role for Asp 32 of MotB. J. Bacteriol. 180: 2729-2735 [Abstract] [Full Text]  
• Scharf, B. E., Fahrner, K. A., Turner, L., Berg, H. C. (1998). Control of direction of flagellar rotation in bacterial chemotaxis. Proc. Natl. Acad. Sci. USA 95: 201-206 [Abstract] [Full Text]