title: Fa1p is a 171 kDa protein essential for axonemal microtubule severing in Chlamydomonas.
abstract: A key event in deflagellation or deciliation is the severing of the nine outer-doublet axonemal microtubules at a specific site in the flagellar transition zone. Previous genetic analysis revealed three genes that are essential for deflagellation in Chlamydomonas. We have now identified the first of these products, Fa1p, a protein required for Ca(2+)-dependent, axonemal microtubule severing. Genetic mapping and the availability of a tagged allele allowed us to physically map the gene to the centromere-proximal domain of the mating-type locus. We identified clones of Chlamydomonas genomic DNA that rescued the Ca(2+)-dependent axonemal microtubule severing defect of fa1 mutants. The FA1 cDNA, obtained by RT-PCR, encodes a novel protein of 171 kDa, which is predicted to contain an amino-terminal coiled-coil domain and three Ca(2+)/calmodulin binding domains. By western analysis and subcellular fractionation, the FA1 product is enriched in flagellar-basal body complexes. Based on these observations and previous studies, we hypothesize that a Ca(2+)-activated, Ca(2+)-binding protein binds Fa1p leading ultimately to the activation of axonemal microtubule severing.
authors.affiliation: Department of Cell Biology and Graduate Program in Biochemistry, Cell and Developmental Biology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Finst
authors.forename: P J
authors.initials: PJ
authors.lastname: Kim
authors.forename: E R
authors.initials: ER
authors.lastname: Griffis
authors.forename: L M
authors.initials: LM
authors.lastname: Quarmby
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D015152:Blotting, Northern; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology; D002147:Calmodulin / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure*; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000032:analysis; D005407:Flagella / Q000502:physiology*; D008868:Microtubule Proteins / Q000235:genetics* / Q000378:metabolism*; D008870:Microtubules / Q000502:physiology*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016296:Mutagenesis / Q000502:physiology; D017433:Protein Structure, Secondary; D012333:RNA, Messenger / Q000032:analysis; D017422:Sequence Analysis, DNA
chemical_list: D001426:Bacterial Proteins; D002147:Calmodulin; D018076:DNA, Complementary; C413984:Fa1 protein, Clamydomonas; D008868:Microtubule Proteins; D012333:RNA, Messenger; D002118:Calcium