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. FXR1 shares high homology with FMR1 and it is located on chromosome 3q28. The 2 main proteins of FXR1 with molecular masses 70 and 78 kDa were detected by western blot analysis. Like FMR1, FXR1 contains 2 KH RNA binding domains as well as nuclear localization and nuclear export signals, and it is believed to shuttle between the cytoplasm and the nucleoplasm. FXR1 is reported to associate with polyribosomes and form homo- and heterodimers with FMR1 and FXR2. Recent studies revealed that FXR1 and AGO2, which are considered as the effectors of translation repression, associate with ARE within the 3′UTR of TNF mRNA and upregulate TNF translation under conditions of serum starvation.