The Role of the Nucleolus in the Transfer of Rna from Nucleus to Cytoplasm

The role of the nucleolus in the transfer of RNA from nucleus to cytoplasm was examined by means of experiments in which inactivation of the whole nucleus, or of the nucleolus, was achieved by a microbeam of ultraviolet light. In heterokaryons in which a chick erythrocyte nucleus had been reactivated, no detectable amount of RNA was transferred from the reactivated nucleus to the cytoplasm of the cell until this nucleus had developed a nucleolus. In HeLa cells, inactivation of the nucleolus alone inhibited the transfer to the cytoplasm, not only of the RNA synthesized at the nucleolar site, but also of the RNA made elsewhere in.the nucleus. It thus appears that the nucleolus governs the transport not only of its own RNA, but also of the RNA which is made on other parts of the chromosomes.