Figure 8

Flagella: to have or to have not. Model for the co-regulation of flagellar assembly (mediated by IFT) and active flagellar disassembly by a common signal, X. Under conditions either permissive or nonpermissive for flagellar assembly, IFT and disassembly are proposed to be mutually antagonistic. Under conditions appropriate for flagellar assembly (Yes), the decision is made to activate IFT and block disassembly at the transition zone. Active IFT could provide a signal to inhibit active disassembly. When flagella are to be disassembled (No), IFT is inactivated. In the absence of IFT, an inhibitory signal would be removed, allowing disassembly to proceed. There may also be direct activation of disassembly.