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Tandem Affinity Purification of Protein Complexes from Eukaryotic Cells

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Tandem stop codons in ciliates that reassign stop codons.

Marie Adachi¹, Andre R O Cavalcanti

¹Biology Department, Pomona College, 175 West 6th Street, Claremont, CA 91711, USA. ma002005@mymail.pomona.edu

Journal of Molecular Evolution

|March 19, 2009

Summary

This summary is machine-generated.

Tandem stop codons, backup genetic signals, were found more often than expected in Paramecium tetraurelia and Tetrahymena thermophila. This suggests higher stop codon read-through in these species due to altered genetic codes.

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Area of Science:

Genetics
Molecular Biology
Evolutionary Biology

Background:

Tandem stop codons are hypothesized genetic backup mechanisms.
While absent in E. coli, they are confirmed in yeast.
Ciliates like Paramecium and Tetrahymena reassign standard stop codons (TAA, TAG) to glutamine.

Purpose of the Study:

To investigate the presence and frequency of tandem stop codons in two ciliate species: Paramecium tetraurelia and Tetrahymena thermophila.
To compare tandem stop codon occurrence in these ciliates with yeast and bacterial systems.

Main Methods:

Genome analysis of Paramecium tetraurelia and Tetrahymena thermophila.
Statistical analysis of tandem stop codon distribution downstream of genes.
Comparison of observed frequencies with those expected based on local base composition.

Main Results:

Both Paramecium and Tetrahymena exhibit a significant excess of tandem stop codons downstream of genes.
The frequency of tandem stop codons is higher in these ciliates than in yeast.
The observed excess is greater than what can be explained by random chance or base composition alone.

Conclusions:

The findings support the presence of tandem stop codons in ciliates with reassigned stop codons.
A higher frequency of stop codon read-through is proposed for Paramecium and Tetrahymena compared to yeast.
This may be attributed to a less efficient translational termination system resulting from stop codon reassignment.