Figure 2.

BBS4 is a flagellar protein required for phototaxis but not IFT. (A) Motion analysis of wild type, bbs4-1, and R26, a strain rescued with a genomic fragment encompassing the BBS4 gene. The direction of light (arrow) is indicated. The radial histograms show the percentage of cells moving in a particular direction relative to the light (24 bins, each 15°). (B) Flagellar length of g1, bbs4-1, bbs7-1, and bbs1-1, as determined by DIC. (C) The velocity of anterograde (a.) and retrograde (r.) IFT particles in wild-type (g1) and bbs4-1 flagella, as determined by DIC. (D) Velocity of KAP-GFP in BBS4 and bbs4-1 flagella, as determined by TIRFM. (C and D) SDs are indicated. (E) Detached flagella from wild type (a–c) or the bbs4-1 mutant (d–f) were stained with anti-IFT46 (a and d) and anti-IFT139 (b and e). (F) Western blot probing proteins of whole cells (a) or isolated flagella (b) with anti-BBS4 (a and b) and anti-IFT139 (a) or anti-IC2, which is specific for an axonemal protein (b), as loading controls. Anti-BBS4 stained a band of ∼41 kD (arrowhead) in whole-cell and flagella samples of wild type and the rescued strain R26; BBS4 was undetectable in bbs4-1. Molecular masses are indicated in kilodaltons. (G) Detached flagella from wild type and the bbs4-1 mutant were stained with anti–acetylated tubulin (ac-tubulin; a and c) and anti-BBS4 (b and d). Bars, 5 µm.