title: Human 18 S ribosomal RNA sequence inferred from DNA sequence. Variations in 18 S sequences and secondary modification patterns between vertebrates.
abstract: We have determined the DNA sequences encoding 18 S ribosomal RNA in man and in the frog, Xenopus borealis. We have also corrected the Xenopus laevis 18 S sequence: an A residue follows G-684 in the sequence. These and other available data provide a number of representative examples of variation in primary structure and secondary modification of 18 S ribosomal RNA between different groups of vertebrates. First, Xenopus laevis and Xenopus borealis 18 S ribosomal genes differ from each other by only two base substitutions, and we have found no evidence of intraspecies heterogeneity within the 18 S ribosomal DNA of Xenopus (in contrast to the Xenopus transcribed spacers). Second, the human 18 S sequence differs from that of Xenopus by approx. 6.5%. About 4% of the differences are single base changes; the remainder comprise insertions in the human sequence and other changes affecting several nucleotides. Most of these more extensive changes are clustered in a relatively short region between nucleotides 190 and 280 in the human sequence. Third, the human 18 S sequence differs from non-primate mammalian sequences by only about 1%. Fourth, nearly all of the 47 methyl groups in mammalian 18 S ribosomal RNA can be located in the sequence. The methyl group distribution corresponds closely to that in Xenopus, but there are several extra methyl groups in mammalian 18 S ribosomal RNA. Finally, minor revisions are made to the estimated numbers of pseudouridines in human and Xenopus 18 S ribosomal RNA.
mesh_terms: D000818:Animals; D001483:Base Sequence; D004275:DNA, Ribosomal / Q000235:genetics*; D006801:Humans; D008745:Methylation; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides / Q000032:analysis; D011560:Pseudouridine / Q000032:analysis; D012335:RNA, Ribosomal / Q000235:genetics*; D013045:Species Specificity; D014981:Xenopus
chemical_list: D004275:DNA, Ribosomal; D009841:Oligonucleotides; D012335:RNA, Ribosomal; D011560:Pseudouridine