Class I release factors in ciliates with variant genetic codes

Area of Science:

• Molecular Biology
• Genetics
• Evolutionary Biology

Background:

• Eukaryotes typically use a single class I release factor (eRF1) to recognize all stop codons (UAA, UAG, UGA) for protein synthesis termination.
• Stop codon reassignment to amino acid codons has occurred independently multiple times in ciliates, necessitating modifications in eRF1 function.
• Understanding these modifications is crucial for deciphering the evolution of the genetic code.

Purpose of the Study:

• To investigate the structural basis of altered stop codon recognition in ciliate eRF1s.
• To compare eRF1 genes from ciliates with variant genetic codes to those from organisms with the universal genetic code.
• To identify potential stop codon-binding regions within eRF1.

Main Methods:

• Amplification, cloning, and sequencing of eRF1 genes from Oxytricha trifallax and Euplotes aediculatus.
• Sequencing and identification of class I RF genes from additional protists and archaea.
• Comparative sequence analysis of eRF1/aRF1 proteins from universal and variant code organisms.

Main Results:

• eRF1 genes from Oxytricha trifallax (UAA/UAG for Gln) and Euplotes aediculatus (UGA for Cys) were sequenced.
• Domain 1 of ciliate eRF1s, specifically the TASNIKS heptapeptide and adjacent regions, showed significant differences compared to universal code eRF1s.
• These variations suggest domain 1 is involved in codon recognition.

Conclusions:

• Domain 1 of eRF1 likely harbors the stop codon recognition site.
• The mechanism of eRF1 codon recognition in ciliates with variant codes may be more intricate than previously proposed.
• This study provides insights into the evolutionary plasticity of the genetic code and protein synthesis machinery.