Nuclear RNA export
- Françoise Stutz1,3 and
- Michael Rosbash2
- 1Institut de Microbiologie, Centre Hospitalier Universitaire Vaudois, 1011 Lausanne, Switzerland; 2Howard Hughes Medical Institute, Department of Biology, Brandeis University, Waltham, Massachusetts 02254 USA
This extract was created in the absence of an abstract.
RNA export is the process by which RNAs are transported to the cytoplasm after synthesis, processing, and RNP assembly within the nucleus. The primary focus of this review is mRNA export with particular attention paid to the yeast Saccharomyces cerevisiae. Because there is rather little known about mRNA export in general and even less about yeast mRNA export, our thinking about the problem is influenced by information from other transport processes. These include not only mRNA export in vertebrate systems but also studies on the export of other RNA substrates and even studies on protein import. Several of these areas of investigation have recently intersected in gratifying ways.
Distinct export pathways for the different classes of RNAs
The first area of investigation to be discussed is the study of RNA export in the Xenopus oocyte system. This approach relies largely on injection experiments, in which different RNA substrates are injected into Xenopus germinal vesicles (nuclei) and cytoplasmic export assayed as a function of time after injection. Pioneering experiments of this kind indicated that the general process of nuclear export is temperature dependent and saturable (Zasloff 1983). Coinjection experiments indicated that different RNA substrates use nonidentical and perhaps entirely different pathways. For example, experiments showed that tRNA, RNA polymerase II gene products (mRNAs and U snRNAs), and ribosomal subunits all used saturable pathways, but any one substrate did not saturate the export of another (Bataille et al. 1990; Jarmolowski et al. 1994; Pokrywka and Goldfarb 1995). Further experiments indicate that U snRNAs also access an export pathway that is shared with both 5S RNA and proteins that carry a specific type of nuclear export signal (NES, see below; Fischer et al. 1995). In higher eukaryotic cells, U snRNAs are exported shortly after synthesis. They pick up snRNP proteins and undergo processing events in the cytoplasm, prior to …
