A nuclear RNA is cut out for translation

Abstract

In this issue of Cell, Prasanth et al. (2005) provide evidence that an inosine-containing RNA that is normally retained in the nucleus is cleaved within its 3' untranslated region following cellular stress. It is then transported to the cytoplasm and translated into protein. These findings suggest that the nucleus may store RNAs destined for translation that then can be released, as needed, in response to specific cellular signals.

Figure 1

The Different Fates of mCAT2 Transcripts (A) Two polyadenylated (A_n) transcripts of the mCAT2 locus are shown. The more abundant CTN-RNA and the mCAT2 mRNA differ only in their 5′UTRs (orange and green, respectively) and an extended 3′UTR unique to CTN-RNA. The proximal and distal polyadenylation sites are indicated (blue) as well as the forward (brown) and reverse inverted repeats (IR, yellow). (B and C) In both unstressed (B) and stressed (C) cells, the mCAT2 mRNA is exported to the cytoplasm and translated to yield mCAT2 protein (gray). In contrast, CTN-RNA is retained in the nucleus in unstressed cells but cleaved in stressed cells to yield a transcript that is exported and translated. Inosine residues from RNA editing are indicated (orange “i”); the question mark signifies that the cleavage site has not been mapped, so it is possible that the forward repeat is in the other fragment.