IC138 is hyperphosphorylated in radial spoke and central pair mutants. To determine whether of the phosphorylation state of IC138 is altered in paralyzed flagellar mutants, axonemes isolated from wild-type, pf17, pf18, mia2-1, bop5-1, and bop5-1pf17 were treated with CIP. (A) Based on a comparison of CIP-treated (-) versus control, untreated (+) axonemes, IC138 seems to be hyperphosphorylated in mia2-1 and the paralyzed mutants pf17, pf18, and bop5-1pf17. In contrast, IC138 from wild type and bop5-1 is not hyperphosphorylated. (B) Flagella were isolated and demembranated immediately preceding the addition of ATP and protease. Microtubule sliding velocity is expressed as micrometers per second.