A common method for analyzing microtubule motor activity is to attach them to a glass coverslip (the tails stick very well to glass) and then incubate with microtubules, which will settle on them and then "glide" across the surface of the coverslip as the heads of the motors propel them. This is easily observable in the light microscope. In an assay such as this, how can one determine the directionality of the movement of the microtubules (plus- or minus-ended)? Assume that you do not know if the motor is a plus- or minus-end motor prior to the experiment.

Explanation:

Microtubules are integral part of the cytoskeleton of eukaryotic cells, responsible for maintaining the shape of the cell. They are involved in intracellular trafficking by forming veritable "rails" along which motor proteins move and transport various organelles.

In analyzing microtubular motor activity, the plus (+) end and the minus(-) end proteins can be marked with non-identical fluorescent proteins, followed by observing it under the fluorescent microscope. From observation, the presence of motility of the fluorescent dye helps to determine if the motor is plus or minus end.