"Headless" kinesin mutants only contain the stalk (middle) and tail domains and can therefore dimerize with their wild-type kinesin partners. However, since they lack the motor (head) domain, the resulting dimers are unable to carry out processive transport of their cargoes and the mutation thus behaves as "dominant negative," meaning that the mutant not only is nonfunctional, but can also interfere with the function of its wild-type counterparts. If a headless mutant of a kinesin heavy chain involved in melanosome movement is overexpressed in fish melanocytes, what would you predict happens in these cells?
A) Pigment dispersion would be inhibited and there would be more tug-of-war between the motors.
B) Pigment aggregation would be inhibited and there would be more tug-of-war between the motors.
C) Pigment dispersion would be inhibited and there would be less tug-of-war between the motors.
D) Pigment aggregation would be inhibited and there would be less tug-of-war between the motors.

Question

Quizplus · Accepted Answer

Kinesins normally carry out the outward transport of melanosomes toward the plus end of microtubules at the cell periphery, by winning a tug-of-war against dyneins that would otherwise transport the pigments back to the center of the cell. The headless mutant inhibits kinesin, resulting in inhibition of the outward movement.

"Headless" Kinesin Mutants Only Contain the Stalk (Middle) and Tail