Transport of functional messenger RNA from liver nuclei in a reconstituted cell-free system.

The reliability of a reconstituted cell-free system for messenger RNA processing and transport, consisting of isolated nuclei in fortified cytosol, has been evaluated in terms of the functionality and regulated release of the transported product. The poly(A) messenger RNA transport in vitro formed appropriate initiation complexes with ribosomes in an optimized translation system and had template activity comparable to that transported in vivo. The intra-nuclear origin of this messenger RNA is supported by pulse-labeling studies, its transport from detergent-treated nuclei and the absence of the release under non-transport conditions. Serum albumin was identified by immunoprecipitation and electrophoresis as one of the products synthesized when the transported RNA was translated in vitro. The transport of messenger RNA in the cell-free system was dependent on specific cytosol (soluble cytoplasmic) proteins. These proteins, which constitutes less than 0.1% of the total cytosol proteins, are precipitated wtih streptomycin with high specificity.