Studies on the Conformation of the 3′Terminus of 18‐S rRNA

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Abstract
The conformation of the 3'' end of 18-S RNA from human, hamster and Xenopus laevis cells was studied. The 3''-terminal oligonucleotide in a T1 RNase digest of 18-S RNA from HeLa [human cervical cancer] cells was identified, using a standard fingerprinting method. The sequence (G)-A-U-C-A-U-U-A, established by Eladari and Galibert for HeLa 18-S rRNA, was confirmed. An identical 3'' terminus is present in hamster fibroblasts and X. laevis cells. The ease of identification of this oligonucleotide has enabled us to quantify its molar yield relative to several other oligonucleotides, and hence to analyze the 3'' terminus by several conformation probes. Its sensitivity to S1 nuclease, limited T1 RNase digestion, bisulfite modification and carbodiimide modification was consistent with the terminal oligonucleotide being in a highly exposed conformation. The .**GRAPHIC**. sequence of 18-S rRNA also appears to be in an exposed location on the basis of 3 of these probes.