Human C-to-U Coding RNA Editing Is Largely Nonadaptive.

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• C-to-U RNA editing converts cytidine to uridine in RNA, potentially altering protein sequences in coding regions.
• Hundreds of C-to-U edited sites exist in humans, but their biological significance remains unclear.
• A prevailing hypothesis suggests nonsynonymous editing offers adaptive, tissue-specific protein regulation.

Purpose of the Study:

• To test the adaptive hypothesis of nonsynonymous C-to-U RNA editing.
• To investigate the biological significance of C-to-U RNA editing in human coding sequences.

Main Methods:

• Comparative analysis of nonsynonymous versus synonymous C-to-U editing frequencies and levels.
• Correlation analysis between editing patterns and gene functional importance or evolutionary constraint.

Main Results:

• Empirical data contradict the adaptive hypothesis, showing lower editing fractions and levels for nonsynonymous sites.
• Nonsynonymous editing frequency decreases with increased gene importance and evolutionary constraint.
• Nonsynonymous editing levels negatively correlate with site evolutionary conservation.

Conclusions:

• The adaptive hypothesis for C-to-U RNA editing is refuted.
• Most C-to-U coding RNA editing events are likely neutral or slightly deleterious, possibly due to off-target enzyme activity.
• This suggests a paradigm shift, viewing posttranscriptional RNA modifications as cellular errors rather than adaptations.