Stop codon recognition in ciliates: Euplotes release factor does not respond to reassigned UGA codon

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• The polypeptide release factor 1 (eRF1) protein is essential for terminating protein synthesis at stop codons in eukaryotes.
• The precise mechanism by which eRF1 decodes stop codons, particularly in organisms with altered genetic codes, remains largely unknown.
• Direct interaction between eRF1 and stop codons is a proposed mechanism for stop codon recognition.

Purpose of the Study:

• To investigate the stop codon recognition capabilities of eRF1 from the ciliate Euplotes aediculatus.
• To determine if ciliate eRF1 can decipher stop codons that have been reassigned to sense codons in their variant genetic code.
• To test hypotheses regarding stop codon discrimination by eRF1.

Main Methods:

• An in vitro translation termination assay was employed using mammalian ribosomes.
• The functionality of Euplotes aediculatus eRF1 was tested against specific stop codons (UAA, UAG, UGA).

Main Results:

• Euplotes aediculatus eRF1 successfully recognized and responded to UAA and UAG as stop codons.
• eRF1 from Euplotes aediculatus failed to recognize the UGA codon, which is reassigned to encode cysteine in this organism.
• This indicates that eRF1's recognition profile is altered in ciliates with variant genetic codes.

Conclusions:

• Ciliate eRF1 exhibits altered stop codon specificity compared to canonical eRF1.
• eRF1 does not recognize stop codons that have been reassigned to sense codons in variant genetic codes.
• These findings support the hypothesis that eRF1 plays a key role in maintaining genetic code integrity, even in organisms with modified codes.