Flagellar radial spokes contribute to the regulation of dynein arm activity and thus the pattern of flagellar bending. They consist of a thin stalk, which is attached to the a subfiber of the outer doublet microtubule, and a bulbous head, which is attached to the stalk and appears to interact with the projections from the central pair of microtubules. The radial spoke head is made of five different polypeptides (RSP1, RSP4, RSP6, RSP9, and RSP10). Radial spoke. Asymmetrically dimethylated at Arg-267 and Arg-398 during flagellum resorption. Probably methylated by PRMT1. Belongs to the flagellar radial spoke RSP4/6 family.