Binds FMN1. Interacts with the Arg/Gly-rich-flanked Pro-rich regions of KHDRBS1/SAM68. Arginine methylation in these regions has no effect on this binding (By similarity). Ubiquitous. Highest levels in spleen and thymus. First detected at 9 dpc. Up-regulated by p53. 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).