Fig 2.

Experimental protocol. Time flows from left to right. (Top row) Protocol A. Cells were grown to the late exponential phase, labeled to saturation with a green fluorescent dye, grown again to the late exponential phase, and labeled with a red fluorescent dye. Three kinds of filaments were observed: type a, filaments with green proximal ends and red distal ends (common); type b, filaments that were entirely green (rare); type c, filaments that were entirely red (common). Initiation of growth of filaments of the latter type occurred after cells had been labeled green. The filaments in the experiments were normal and helical; for simplicity, they are shown here as straight. (Bottom row) Protocol B. Protocol B is the same as protocol A, except an aliquot of cells that had been labeled green was subjected to viscous shear; two of the filaments shown were shortened, and one was not. The parent population for the cells that were sheared was the population studied in protocol A, so a record was made of cells both before and after shearing.