Position-dependent termination and widespread obligatory frameshifting in Euplotes translation

Area of Science:

• Molecular Biology
• Genetics
• Evolutionary Biology

Background:

• Programmed ribosomal frameshifting is a rare translational event.
• Ribosomes can alter their reading frame during protein synthesis.
• Complex mRNA signals typically support frameshifting.

Purpose of the Study:

• Investigate frameshifting events at stop codons in ciliates.
• Determine the role of stop codons in translation termination in Euplotes.
• Analyze the evolutionary plasticity of frameshifting.

Main Methods:

• Analysis of frameshifting at stop codons in Euplotes crassus and Euplotes focardii.
• Identification of codons preceding stop signals and frameshift types (+1, +2).
• Assessment of frameshift influence on translation rates and evolutionary patterns.

Main Results:

• Widespread frameshifting observed at stop codons in Euplotes.
• 47 different codons induced +1 or +2 frameshifts, with AAA being most frequent for +1.
• Stop codon proximity to the 3' mRNA end, not sequence context, signals termination.
• Frameshifts exhibited plasticity and rapid evolution with minimal impact on translation rates.

Conclusions:

• Stop codons are not sufficient signals for translation termination in Euplotes.
• The default function of stop codons in Euplotes is frameshifting.
• Termination is position-dependent and may require additional factors.