Fig. 4.

Growth of a thick actin bundle in a myosin II-null cell. (A) The bundle labeled with LimEΔcoil-GFP and viewed by TIRF microscopy extends in line with the layout of the actin network. At 3.5 sec, the bundle reaches its maximal length of 6 μm. Thereafter, ≈15 sec are needed for disassembly. (Scale bar: 5 μm.) (B) Line scan of fluorescence intensities along the actin bundle shown in A, sampled at 100-msec intervals from the 0- to 2.4-sec frames in the direction of the arrow. The front of the bundle is characterized by a steep intensity gradient that advances at an average velocity of 1.7 μm·sec^–1.