Open AccessNucleotide sequence of an external transcribed wacer inXenopus laevisrDNA: sequences flanking the 5' and 3' ends of 18S rRNA are non-complementary
Author(s) -
B.E.H. Maden,
Michael Moss,
Mohammad Salim
Publication year - 1982
Publication title -
nucleic acids research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 9.008
H-Index - 537
eISSN - 1362-4954
pISSN - 0305-1048
DOI - 10.1093/nar/10.7.2387
Subject(s) - biology , xenopus , genetics , nucleic acid sequence , internal transcribed spacer , ribosomal rna , ribosomal dna , sequence (biology) , nucleotide , 5' flanking region , spacer dna , base sequence , transfer rna , microbiology and biotechnology , dna , gene , phylogenetics , rna , promoter , gene expression
We have sequenced the external transcribed spacer (ETS) of a ribosomal transcription unit from Xenopus laevis, together with sections of the preceding non-transcribed spacer. Our analysis was carried out on the same cloned transcription unit as that from which the internal transcribed spacers (ITS) were previously sequenced. The ETS is approximately 712 nucleotides long and, like the ITS regions, is generally very rich in C plus G. Features of the sequence include an excess of oligo-C tracts over oligo-G tracts and a tract of 37 nucleotides consisting almost entirely of G and A residues. Parts of the sequence can give rise to stable internal secondary structures. However, in contrast to Escherichia coli, there is no potential for major base-pairing between the 18S flanking regions of the ETS and ITS. Further findings are that there are no initiation (ATG) codons in the ETS and that, as in other X.laevis rDNA cloned units, the sequence preceding the ETS is duplicated, with a few changes, in the "Bam island" sequence of the non-transcribed spacer.