The enduring enigma of nuclear translation

Abstract

Although the physical separation of transcription in the nucleus and translation in the cytoplasm has presided as a fundamental tenet of cell biology for decades, it has not done so without recurring challenges and contentious debate. In this issue, David et al. (2012. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201112145) rekindle the controversy by providing convincing experimental evidence for nuclear translation.

Figure 1.

Potential roles of nuclear ribosomal activity. We suggest three general classes of potential activities for nuclear ribosomes. First is bona fide protein synthesis, in which mature proteins (likely those that are functional in the nucleus) are synthesized on polyribosomes. A second possibility is that nuclear ribosomes participate in a quality control process, either of mRNAs or of the ribosomes themselves. Depicted is the removal of the exon junction complex in NMD, a process that targets mRNAs with premature stop codons for degradation. A final possibility is that ribosomes react with RNA substrates in a nonspecific manner while in the nucleus, producing proteins with no particular coherence.