Ring Finger And KH Domain Containing Protein 4 (RKHD4)

Like the other human MEX3 proteins, the deduced 520-amino acid MEX3A protein has an N-terminal nuclear export signal (NES), 2 heterogeneous nuclear ribonucleoprotein K (HNRNPK) homology (KH) domains, and a C-terminal RING finger domain. The KH domains are present in C. elegans Mex3, but not the RING domain. RT-PCR detected variable expression of MEX3A in human tissues and cell lines, with highest levels in fetal brain and testis.RNA homopolymer-binding assays and immunoprecipitation analysis revealed that MEX3A, MEX3B, and MEX3C bound RNA via their KH domains in vitro and in vivo. Immunofluorescence analysis of transfected breast cancer cells showed that MEX3A, MEX3B, and MEX3C shuttled between the nucleus and cytoplasm in an NES-dependent manner.