Tandem Stop Codons in Ciliates That Reassign Stop Codons |
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Authors: | Marie Adachi Andre R O Cavalcanti |
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Institution: | (1) Biology Department, Pomona College, 175 West 6th Street, Claremont, CA 91711, USA |
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Abstract: | Tandem stop codons are extra stop codons hypothesized to be present downstream of genes to act as a backup in case of read-through
of the real stop codon. Although seemingly absent from Escherichia coli, recent studies have confirmed the presence of such codons in yeast. In this paper we will analyze the genomes of two ciliate
species—Paramecium tetraurelia and Tetrahymena thermophila—that reassign the stop codons TAA and TAG to glutamine, for the presence of tandem stop codons. We show that there are more
tandem stop codons downstream of both Paramecium and Tetrahymena genes than expected by chance given the base composition of the downstream regions. This excess of tandem stop codons is
larger in Tetrahymena and Paramecium than in yeast. We propose that this might be caused by a higher frequency of stop codon read-through in these species than
in yeast, possibly because of a leaky termination machinery resulting from stop codon reassignment. |
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Keywords: | Tandem stop codons Translation termination Alternative genetic codes stop codon reassignment Ribosome read-through Tetrahymena Paramecium |
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