Intracellular transport of microinjected 5S and small nuclear RNAs.

The mechanism by which some RNAs are segregated in the cell nucleus was analysed by microinjecting 32 P-labelled total RNA from HeLa cells into the cytoplasm of Xenopus oocytes. Small nuclear RNAs (u1, U2, U4, U5 and U6) migrated into the cell nucleus, where they became 30-60 fold more concentrated than in the cytoplasm. Other RNAs, such as tRNA and 7S RNA, remained in the cytoplasm, while 5S RNA became concentrated in the nucleolus. Studies with lupus erythematosus antibodies showed that the migrating RNAs become associated with oocyte RNA-binding proteins.