Functional recombination of outer dynein arms with outer arm-missing flagellar axonemes of a Chlamydomonas mutant

Abstract

ABSTRACT A flagellar mutant of Chlamydomonas, oda, lacks the entire outer dynein arm but can swim at a speed of one third to half of that of the wild type. We found that the addition of a high-salt extract of wild-type axonemes to demembranated oda cell models restored up to 83 % of the outer arms normally present on the outer-doublet microtubules of wild-type axonemes. Furthermore, when reactivated in the presence of ATP after being mixed with the extract, the oda cell models gained a higher level of motility, close to that of the wild type. The increase in flagellar beat frequency parallelled the increase in the number of restored outer dynein arms. These observations indicate that the axoneme of the oda mutant retains the binding sites for the outer dynein arms, and that the outer arms solubilized with high salt are functionally active. This in vitro recombination system with the oda mutant should be useful as an assay system for various preparations of outer-arm dynein. Evidence is presented that the two axonemes on an oda cell model beat at the same frequency, whereas those on a wild-type model beat at different frequencies. The two oda axonemes beat at the same frequency even after the higher level of motility has been restored by addition of crude dynein extract. We propose that a heterogeneity in the outer dynein arms is responsible for the frequency imbalance between the two flagella of wild-type Chlamydomonas.