Figure 1.

Spindle microtubules incorporate bovine rhodamine-tubulin. (A) DIC mode image of a crane-fly spermatocyte at metaphase made 45 s after a 4-s pulse (∼1 picoliter) injection of 30 μM rh-tubulin. This optical section includes portions of all three bivalents and one of the kinetochore fibers attached to the middle bivalent is in sharp focus (arrowhead). (B and C) Wide-field fluorescence mode images of the cell in A, revealing fluorescence incorporation into kinetochore fibers initially at the kinetochores (arrowheads in B) and then spreading poleward with time (arrowheads in C). (B) 1 min after injection; (C) 10 min after injection. (D) Another DIC mode image made 13 min after injection illustrating a different optical section and additional kinetochore fibers (arrowheads) in sharp focus. Bar, 10 μm.