Biochemical depletion of CK1 rescues microtubule sliding in isolated pf17 axonemes, and this rescue requires I1 dynein. (A) Experimental strategy to test the role of CK1 in microtubules. (B) ATP-induced microtubule sliding velocity was measured in isolated axonemes, CK1-depleted axonemes, or CK1-depleted axonemes reconstituted with purified rCK1 (Okagaki and Kamiya, 1986; Wirschell et al., 2009). The effect of DRB/CK1-7 and the phosphatase inhibitor microcystin-LR (MC) was also examined. The bars represent: (1) wild-type (WT) axonemes; (2) WT axonemes depleted of CK1 (note that there is no change in velocity); (3) pf17 axonemes (note the slow, baseline sliding velocity); (4) pf17 axonemes plus DRB; (5) pf17 axonemes plus CK1-7; (6) pf17 axonemes plus DRB and microcystin-LR; (7) pf17 axonemes plus CK1-7 and microcystin-LR; (8) pf17 axonemes depleted of CK1 (note the rescue of microtubule sliding); (9) pf17 axonemes depleted of CK1 plus microcystin-LR; (10) ida1pf17 axonemes; (11) ida1pf17 axonemes plus DRB; (12) ida1pf17 axonemes plus CK1-7; and (13) ida1pf17 axonemes depleted of CK1 (note the failure in rescue of sliding). Microtubule sliding velocity is expressed as µm/s, and means and standard deviations (error bars) were calculated from at least three independent experiments with a minimum sample size of 75 axonemes.