Aromatic thioethers of purine nucleotides

Export of ribosomal subunits from resealed rat liver nuclear envelopes

We have previously described the rat liver resealed nuclear envelope model system for the study of the selective import of nuclear proteins, and the export of poly(A)-containing mRNA [Riedel, N., Bachmann, M., Richter, H. & Fasold, H. (1987) Proc. Natl Acad. Sci. USA 83, 3540-3544]. The vesicles still respond to the importin-ATP signal for the uptake of nuclear-location-sequence (NLS)-carrying proteins. During the preparation of the vesicles and extraction of the chromatin from nuclei in cold hypotonic heparin solution, ribosomal subunits may be introduced into these envelopes, and after resealing remain stably included. Efflux from the resealed nuclear envelopes is effected by a cytoplasmatic protein fraction, and strongly enhanced in the presence of ATP. The heterogeneous nuclear RNP (hnRNP) A1, the components of importin, or GTP showed no influence on this export. The ATP-dependent efflux of mRNA is not affected by these cytoplasmic proteins in this model system.

Cross-linking of nucleic acids to proteins. Modified poly(A) as mRNA for Escherichia coli ribosomes

Poly(adenylic acid) was modified by methylchlorotetrolic ester in a reproducible and defined content of the derivatized bases. The nucleic acid derivative is protein reactive and was coupled to 70S ribosomes from Escherichia coli, in order to identify proteins along the mRNA pathway. The binding of the label becomes specific under the direction of tRNA(Lys) and is then almost exclusively located on the small subunit. The proteins S1, S12, S18 and S21 were labeled, as shown by an antibody assay. The yield of the affinity label was 5.4%, as calculated from the labeled nucleic acid. This compares favourably with the yields from photolabile compounds.

Preparation and characterization of nuclear-envelope vesicles from rat liver nuclei

We describe a procedure for the preparation of sealed nuclear-envelope vesicles from rat liver nuclei. These vesicles are strikingly similar in their polypeptide composition when compared with those of nuclear envelopes prepared conventionally using deoxyribonuclease I. Subfractionation analysis by means of extraction with high salt and urea show that the components of the nuclear envelope, e.g. the pore-complex/lamina fraction, are present. The residual DNA content is only 1.5%, and typical preparations consist of about 80% vesicles, with the vesicular character of these envelopes shown by microscopic and biochemical studies. The vesicles can be obtained in high yield, are tight and stable for at least two days and are enriched in a nucleoside triphosphatase thought to be involved in nucleocytoplasmic transport processes. Because the vesicles are largely free of components of the nuclear interior, but retain properties of intact nuclei, we believe that they are a valuable model system to study nucleocytoplasmic transport. Although in transport studies with isolated nuclei interference from intranuclear events has to be considered, the nuclear-envelope vesicles provide the possibility of studying translocation alone. Furthermore, the less complex nature of these vesicles compared with whole nuclei should facilitate investigation of the components involved in the regulation of nuclear transport processes.