Nucleotide sequence of a ribosomal RNA gene intron from slime mold Physarum polycephalum.

The Physarum polycephalum 26S ribosomal RNA gene contains two intervening sequences (introns). The DNA sequence of one of these introns was analyzed together with that of its flanking regions (exons). In addition, the nucleotide sequence of the corresponding region of the reverse transcript of 26S rRNA was determined, and from comparisons of both sequences the precise location and size of the intron were determined. Our findings, when compared with those for Tetrahymena and Chlamydomonas rRNA gene introns, led to the conclusion that certain characteristics exist near the ends of these introns. (i) An exon ends in T at the exon/intron junction and an intron ends in G at the intron/exon junction in all cases. (ii) For each intron, direct repeats several nucleotides long are present 5 to approximately 30 nucleotides upstream from both the exon/intron and intron/exon junctions.