The nucleotide sequences of 5.8-S ribosomal RNA from Xenopus laevis and Xenopus borealis.

1. The nucleotide sequence of 5.8-S rRNA from Xenopus laevis is given; it differs by a C in equilibrium U transition at position 140 from the 5.8-S rRNA of Xenopus borealis. 2. The sequence contains two completely modified and two partially modified residues. 3. Three different 5' nucleotides are found: pU-C-G (0.4) pC-G (0.2) and pG (0.4). 4. The 3' terminus is C not U as in all other 5.8-S sequences so far determined. 5. The X. laevis sequence differs from the mammalian and turtle sequences by five and six residue changes respectively. 6. A ribonuclease-resistant hairpin loop is a principle feature of secondary structure models proposed for this molecule. 7. Sequence heterogeneity may occur at one position at a very low level (approximately 0.01) in X. laevis 5.8-S rRNA, while none was detected in X. borealis or HeLa cell 5.8-S rRNA.