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A switch-complex protein involved in reception of phosphorylated CheY and control of rotational bias.

Binding of phosphorylated CheY changes the switch’s rotational bias. A change in bias alters the balance of swimming behaviours without requiring the motor to sense external attractant directly. ^[ref]

M. Silverman coauthored the 1974 demonstration that bacterial flagella drive motility by rotation. Antibody-mediated attachment of a flagellum to a surface made the bacterial body rotate instead, turning an otherwise difficult-to-observe motor movement into a visible cellular motion.^[ref][ref]

The experiment illustrates a mechanical strategy: constrain one member of a moving assembly and observe the resulting motion of the other. It supplied evidence for a rotary motor rather than requiring flagellar propulsion to be inferred only from the swimming trajectory.

S. H. Larsen led the 1974 study connecting changes in bacterial flagellar motor rotation direction to chemotaxis. Tethered-cell observations made motor rotation visible, allowing responses to chemical stimuli to be related to switching behavior rather than only to the net movement of a swimming bacterium.^[ref]

The distinction is useful because directional migration need not mean that a cell points toward a stimulus and moves straight to it. Modulating movement and reorientation can bias a trajectory statistically. The publisher's original byline identifies S. H. Larsen as Steven H. Larsen.