Transport of a novel complex in the cytoplasmic matrix of Chlamydomonas  flagella

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Abstract
Proteins necessary for maintenance and function of eukaryotic flagella are synthesized in the cell body. Transport of the inner dynein arm subunit p28 IDA4 in Chlamydomonas flagella requires the activity of the kinesin KHP1 FLA10 , a protein inactive at restrictive temperature in fla 10, a temperature-dependent mutant of flagellar assembly. To identify other molecules involved in active transport of inner dynein arms within flagella we searched for polypeptides of the cytoplasmic matrix of flagella that fulfill two conditions: they bind to p28 and require the activity of KHP1 to be present in flagella. We found that the cytoplasmic matrix of flagella contains a previously unidentified “17S” complex of at least 13 polypeptides that in part is associated with p28. The 17S complex is present at permissive but not at restrictive temperature in fla 10 flagella. It also turns over in the cytoplasmic matrix more frequently than dynein arms within the axoneme. This evidence suggests that the 17S complex transports precursors of inner dynein arms within flagella.