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Title: Nucleotide sequence from a ribosomal RNA transcription unit of Xenopus laevis
Author: Hall, Lucinda M. C.
ISNI:       0000 0001 3526 7563
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1981
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I have determined the sequence of the central part of a ribosomal transcription unit from Xenopus laevis, using the plasmid pXlr101. The sequence comprises over 200 bp at the 3' end of the 18S gene, the first internal transcribed spacer, the 5.8S gene, the second internal transcribed spacer, and over 100 bp at the 5' end of the 28S gene. The two transcribed spacers have G + C contents of over 80% and include long homopolymeric tracts of G or C (10-15 residues). ITS1 also has long tracts of purines containing several A residues. The Xenopus sequence is compared to other organisms where data is available. The gene sequences show a high level of homology with sequences from other eukaryotes and also some homology with the prokaryote E. coli. No sequence homology is found between the internal transcribed spacers of Xenopus and yeast (Saccharomyces). Tentative secondary structure models are proposed for the Xenopus sequence and again compared to possible models from other organisms. Secondary structure may be highly conserved within the mature rRNAs, even in regions where the primary sequence is variable between species. In the transcribed spacers one hairpin may be held in common by Xenopus and yeast but other secondary structures are not obviously conserved. I have attempted to characterise some ribosomal RNA precursors in Xenopus tissue culture cells by both 'Northern' transfers and SI nuclease protection mapping. Various artifacts limit the usefulness of these techniques in this system. However it is proposed that a putative '30S' precursor exists containing the RNA of 5.8S, ITS2 and 28S, and having the same 5' end as 5.8S rRNA. Evidence from the sequence supports the proposition that 5.8S rRNA in eukaryotes is structurally equivalent to the 5' end of 23S rRNA in E. coli The results lead to speculation of the relationship between rRNA processing in eukaryotes and E. coli.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Genetics