The fragile X mental retardation 1 protein (FMR1) is a cytoplasmic RNA binding protein abundantly expressed in the brain neurons. The absence of FMR1 protein leads to fragile X syndrome. FMR1 has 2 paralogs known as FXR1 and FXR2. FXR2 shares high homology with FMR1 and it is located on chromosome 17p13.1. Like FMR1, FXR2 has 2 KH RNA binding domains as well as a nuclear localization and a nuclear export signals. In contrast to FMR1 and FXR1, which shuttle between cytoplasm and nucleoplasm, FXR2 shuttles between cytoplasm and nucleolus, and it most likely transports different RNA species. Continuous rRNA transcription is considered to be necessary for the import of FXR2 into the nucleus and its maintenance in the nucleolus. FXR2, which is very similar to FMR1, also associates with translating polyribosomes and forms homo- and heterodimers with FMR1 and FXR1.