A hallmark of translation initiation is joining of the small and large ribosomal subunits on the mRNA. Although the 40S and 60S subunits are synthesized and assembled in the nucleolus in eukaryotes, it is believed that there are mechanisms that kept them inactive, preventing 80S assembly and translation in the nucleus. The consensus is that translation occurs only in the cytoplasm. Contrary to this view, we have recently reported that translating 80S ribosomes are also present in the nucleolus and other nuclear sites in Drosophila (1). By employing our 80S reporter technique coupled to flow cytometer analysis of Drosophila cells, we have observed that nuclear 80S are most apparent during S phase. Furthermore, increased levels of nuclear 80S were observed upon serum starvation and other forms of cellular stress. Our observations suggest a role for nuclear translation during cellular stress.
1: Al-Jubran et al. Visualization of the joining of ribosomal subunits reveals the presence of 80S ribosomes in the nucleus. RNA. 2013.