Abstract
A novel Chlamydomonas flagellar mutant (oda-11) missing the alpha heavy chain of outer arm dynein but retaining the beta and gamma heavy chains was isolated. Restriction fragment length polymorphism analysis with an alpha heavy chain locus genomic probe indicated that the oda-11 mutation was genetically linked with the structural gene of the alpha heavy chain. In cross-section electron micrographs, the oda-11 axoneme lacked the outermost appendage of the outer arm, indicating that the alpha heavy chain should be located in this region in the wild-type outer arm. This mutant swam at 119 microns/s at 25 degrees C, i.e., at an intermediate speed between those of wild type (194 microns/s) and of oda-1 (62 microns/s), a mutant missing the entire outer dynein arm. The flagellar beat frequency (approximately 50 Hz) was also between those of wild type (approximately 60 Hz) and oda-1 (approximately 26 Hz). These results indicate that the outer dynein arm of Chlamydomonas can be assembled without the alpha heavy chain, and that the outer arm missing the alpha heavy chain retains partial function.
Highlights
(oda-11) missing the ot heavy chain of outer arm dynein but retaining the/3 and 3~ heavy chains was isolated
Because we wanted to isolate mutants with more subtle defects in dynein arms, we looked for mutants whose swimming speed was only slightly lower than that of the wild type
SDS-PAGE analyses of the axonemes from these clones showed that one clone was missing the el heavy chain of outer arm dynein (Fig. 1)
Summary
(oda-11) missing the ot heavy chain of outer arm dynein but retaining the/3 and 3~ heavy chains was isolated. The flagellar beat frequency (,x,50 Hz) was between those of wild type (~,60 Hz) and oda-1 (,x,26 Hz) These results indicate that the outer dynein arm of Chlamydomonas can be assembled without the ot heavy chain, and that the outer arm missing the e~ heavy chain retains partial function. Electron microscope studies have shown that the isolated outer arms have bouquet-like structures in which two or three heads are connected through a thin stem to a common base (Johnson and Wail, 1983; Witman et at., 1983; Goodenough and Heuser, 1984; Sale et al, 1985) Each of these heads appears to be composed of a heavy chain, because the number of the heads equals that of the heavy chains. Because this mutant can swim at an intermediate speed between the speeds of the wild type and a mutant (oda) missing the entire outer arm, the mutant outer arm appears to retain some functional activity
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