Radial spoke 3 (RS3), when present, is the most distal of each group of radial spokes, whether grouped as triplets or doublets. RS3 has significantly different morphology and protein composition than RS1 and RS2 and also extends at a slant from the microtubule doublet, rather than perpendicularly like RS1 and RS2. In some organisms (e.g. Chlamydomonas and Sarcophaga bullata), RS3 is represented only as a stump attached to the A-microtubule lacking the rest of the stalk structure and entirely lacking the head structure.
RS3