Evidence for interactions between MotA and MotB, torque-generating elements of the flagellar motor of Escherichia coli.

Cells that overexpress MotA (encoded on a plasmid derived from pBR322) grow slowly because of proton leakage. We have traced this defect to the coexpression of a fusion protein consisting of 60 amino acids from the N terminus of MotB and 50 amino acids specified by pBR322. Mutations within the N terminus, known to abolish function when present in full-length MotB, reversed the growth defect. Growth also was normal when MotA was coexpressed with wild-type MotB or with a series of MotB N-terminal fragments.