Coupled Transcription and Translation Within Nuclei of Mammalian Cells

• DOI: 10.1126/science.1061216
• Publication Date: 2002-07-27T05:39:52Z
• Authors: Francisco J. Iborra; Dean A. Jackson; Peter R. Cook
• Keywords: Boron Compounds; Cell Nucleus; Protein Synthesis Inhibitors; Cytoplasm; 0303 health sciences; Cell Membrane Permeability; Biotin; Proteins; Cell Fractionation; Immunohistochemistry; Fluorescence; Mitochondria; Protein Transport; 03 medical and health sciences; Protein Biosynthesis; COS Cells; Animals; Autoradiography; Humans; RNA Polymerase II; Cycloheximide; HeLa Cells

It is widely assumed that the vital processes of transcription and translation are spatially separated in eukaryotes and that no translation occurs in nuclei. We localized translation sites by incubating permeabilized mammalian cells with [ 3 H]lysine or lysyl–transfer RNA tagged with biotin or BODIPY; although most nascent polypeptides were cytoplasmic, some were found in discrete nuclear sites known as transcription “factories.” Some of this nuclear translation also depends on concurrent transcription by RNA polymerase II. This coupling is simply explained if nuclear ribosomes translate nascent transcripts as those transcripts emerge from still-engaged RNA polymerases, much as they do in bacteria.