Figure 4.

KIF3CC modulates the taper of extending MT tips. (A) Compiled data for tip fluorescence deviation measurements for the no-motor control and 50 nM KIF3CC as a function of extension length. Data were collected using the TipTracker algorithm for MATLAB on inversely labeled MTs (bright extensions at a ratio of 1:2 of X-Rhodamine labeled to unlabeled tubulin; dim seeds with a ratio of 1:8.5 of X-Rhodamine labeled to unlabeled tubulin). Fluorescence deviation was defined as half of the distance over which the fluorescence signal depletes at the MT tip from maximum intensity to background, as shown by the red bar in the overlay of representative 3-μm MT extension profiles from the KIF3CC (red) and no motor (gray) conditions (inset). As illustrated, the presence of KIF3CC results in protofilaments with a lower fluorescence deviation than the no-motor control. (B) Average MT extension profiles for increasing extension lengths, illustrated by a progressive grayscale value with short MT extensions (0.5 μm) in black and the longest extensions (up to 5 μm) in light gray. Normalized intensity values are plotted as a function of MT extension length in the no-motor control and in the presence of 50 nM KIF3CC. Datapoints along each trace for the no-motor control as well as the 0.5–2 μm extension traces for KIF3CC represent the average of six extensions. The 3-μm trace for KIF3CC was limited to N = 3 due to the limited population that reach this range. Error bars represent mean ± SE of the normalized intensity values from the averaged traces. (C) Distribution of the population of MT extension lengths in the absence and presence of 50 nM KIF3CC. This bar graph represents the dataset used to estimate fluorescence deviations in (A). To see this figure in color, go online.