Fa1p Is a 171 kDa Protein Essential for Axonemal Microtubule Severing in Chlamydomonas

J Cell Sci. 2000 Jun;113 ( Pt 11):1963-71.


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.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Blotting, Northern
  • Calcium / metabolism
  • Calcium Signaling / physiology
  • Calmodulin / metabolism
  • Chlamydomonas reinhardtii / genetics*
  • Chlamydomonas reinhardtii / metabolism
  • Chlamydomonas reinhardtii / ultrastructure*
  • Chromosome Mapping
  • Cloning, Molecular
  • DNA, Complementary / analysis
  • Flagella / physiology*
  • Microtubule Proteins / genetics*
  • Microtubule Proteins / metabolism*
  • Microtubules / physiology*
  • Molecular Sequence Data
  • Molecular Weight
  • Mutagenesis / physiology
  • Protein Structure, Secondary
  • RNA, Messenger / analysis
  • Sequence Analysis, DNA


  • Bacterial Proteins
  • Calmodulin
  • DNA, Complementary
  • Fa1 protein, Clamydomonas
  • Microtubule Proteins
  • RNA, Messenger
  • Calcium