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The complete nucleotide sequences of the 5.8S and 26S rRNA genes of Physarum polycephalum and the transcribed spacer between them were determined. Comparison of the sequences with those of the Escherichia coli 23S rRNA and yeast 26S rRNA genes showed that there are 16 highly homologous regions in the sequences of Physarum and E. coli and that eukaryotes have some eukaryote-specific extra sequences. The sequence immediately following the 5.8S-like region of E. coli 23S rRNA was found to be highly homologous to the 5' terminus of Physarum 26S rRNA, indicating that the eukaryote-specific 5.8S rRNA gene is derived from the 5'-terminal region of the prokaryote large rRNA gene.
Otsuka et al. (Wed,) studied this question.