Genetic evidence for a switching and energy-transducing complex in the flagellar motor of Salmonella typhimurium

Abstract

The flaAlI.2, flaQ, and flaN genes of Salmonella typhimurium are important for assembly, rotation, and counterclockwise-clockwise switching of the flagellar motor. Paralyzed and nonchemotactic mutants were subjected to selection pressure for partial acquisition of motility and chemotaxis, and the suppressor mutations of the resulting pseudorevertants were mapped and isolated. Many of the intergenic suppressor mutations were in one of the other two genes. Others were in genes for cytoplasmic components of the chemotaxis system, notably cheY and cheZ; one of the mutations was found in the cheA gene and one in a motility gene, motB. (14), i.e., it contains a binary switch. The switch operates even in unstimulated cells; stimijli bias the switching events in a way that results in migration toward more favorable environments (3, 17).The motors are located at the cell surface. After digestion of the peptidoglycan layer and dissolution of the outer and cytoplasmic membranes, a structure can be isolated which is termed the flagellar basal body and consists of four rings and a rod (7,8). A variety of evidence, including a recent study of Salmonella typhimurium (1), indicates that the basal body is not the entire motor. It does not contain any of the proteins known to be involved in the two central functions of the motor, conversion of proton motive force into rotational work and switching between the two rotational senses.Five proteins are known to play important roles in rotation and switching. They are MotA and MotB (6,9,25,28,29,33) and FlaAII.2, FlaQ, and FlaN (4,5,9,11,12,19,22,23,26,[31][32][33]

EnvZ-OmpR Interaction and Osmoregulation in Escherichia coli

“…However it is important to know that CheA belongs to Class II histidine kinases, whereas EnvZ belongs to Class I, the major signal transducing kinases in E. coli as 29 of 30 histidine kinases in E. coli belong to Class I (46). Class II kinases are involved in regulating flagella rotation whereas Class I kinases regulate transcription of specific genes (47). The present report is the first to accurately estimate the cellular contents of a Class I kinase and its cognate response regulator, suggesting that the Class I kinase system is substantially different from the Class II kinase system in their regulatory mechanisms.…”

Putative channel components for the fast-rotating sodium-driven flagellar motor of a marine bacterium

“…Five proteins, MotA, MotB, FliG, FliM, and FliN, appear to be involved in force generation of proton-driven motors. It has been proposed that FliG, FliM, and FliN make a switch complex and function as the rotor of the flagellar motor (27,51). They form the C ring, which was newly found on the cytoplasmic face of the MS ring (13,53).…”

Evidence for symmetry in the elementary process of bidirectional torque generation by the bacterial flagellar motor

“…FliG, FliM, and FliN are also called the switch proteins responsible for switching the direction of motor rotation because certain mutations in these proteins affect the switching between CW and CCW rotation (15). The switching probability is modified by a chemotactic signal transduction pathway (1,6).…”