Sequence of a ribosomal RNA gene intron from Tetrahymena

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Abstract
Recently, several genes coding for messenger RNA, transfer RNA and ribosomal RNA in eukaryotes have been found to be interrupted in their coding regions by DNA sequences which are not represented in the mature RNA transcripts (see ref. 1 for review). Many of these intervening sequences, or introns2, are now known to be transcribed in the precursor RNA, from which they are subsequently processed out to form the mature RNA3–10. As the intron–exon junctions must in some way be recognised for accurate splicing, the nucleotide sequences of these regions from a number of protein-coding and tRNA genes have been analysed11–18. Sequence homologies were found at the splice points of the protein-coding gene introns from diverse organisms12,13, but the tRN A intron boundaries were not similar to these14,15. This has led to the speculation that different splicing activities are necessary for the processing of introns in mRN A and tRN A precursors19. We report here the sequence of a ribosomal RNA gene intron from Tetrahymena in which intron–exon junctions differ from those analysed to date.