Altered restriction of nuclear RNA during incubation in vitro

Nuclei were isolated from rat liver and incubated $\text{in}\text{vitro}$ in two commonly employed RNA transport assays. Released ¹⁴C] RNA was isolated and hybridized with filter-bound DNA in the presence of competing cytoplasmic RNA. A significant portion of RNA which was transported to either medium was not represented in cytoplasmic RNA. These results indicate that the restriction of some sequences to the nucleus $\text{in}\text{vivo}$ is not maintained $\text{in}\text{vitro}$.