Lariat intronic RNAs in the cytoplasm of vertebrate cells

Introns are non-coding DNA sequences interspersed among the coding sequences of genes. Shortly after transcription, the intronic sequences are spliced out of the primary RNA transcript as lariat RNAs (circular molecules with a short tail). Most of these lariats are destroyed within minutes in the cell nucleus. We report here that many such intronic RNAs are, in fact, exported to the cytoplasm, where they remain as stable circular molecules. These cytoplasmic introns are derived from hundreds of different genes of widely different functions. We find them in cells of human, mouse, chicken, frog, and zebrafish. The widespread occurrence of so many stable lariat RNAs in the cytoplasm suggests that they play some as yet unexpected role in cell metabolism.