Binds FMN1. Interacts with the Arg/Gly-rich-flanked Pro-rich of KHDRBS1/SAM68. Arginine methylation in these regions has no effect on this binding. Highly expressed in the eye. These WW domains interact with Arg/Gly-rich-flanked Pro-rich domains found in several WW domain-binding proteins (WBPs). The N-terminal WW domain has the greater ligand-binding ability (By similarity). Extended N-terminus.