It has been suggested that NMD3 is a cytoplasmic factor required for a late cytoplasmic assembly step of the 60S subunit but is not a ribosomal protein. A mutation in NMD3 was found to be lethal in the absence of XRN1, which encodes the major cytoplasmic exoribonuclease responsible for mRNA turnover. The NMD3 protein sequence does not contain readily recognizable motifs of known function. However, NMD3 orthologues display an amino-terminal domain containing four repeats of Cx2C, reminiscent of zinc-binding proteins, implicated in nucleic acid binding or protein oligomerization.