Revisiting the Saccharomyces cerevisiae predicted ORFeome

Area of Science:

• Genomics
• Molecular Biology
• Yeast Biology

Background:

• Defining an organism's complete set of protein-encoding genes (ORFeome) is crucial for understanding its biology.
• ORFeome annotation relies on computational predictions and experimental validation.
• Recent annotation updates in Saccharomyces cerevisiae removed 'orphan' ORFs lacking cross-species conservation.

Purpose of the Study:

• To re-evaluate the functional potential of Saccharomyces cerevisiae orphan ORFs.
• To determine if orphan ORFs, previously excluded due to low sequence conservation, encode functional products.
• To propose revised criteria for ORFeome annotation.

Main Methods:

• Analysis of transcripts and translated products from functional genomics and proteomics data for orphan ORFs.
• Application of a naïve Bayes model to predict ORF functionality.
• Experimental verification of strand-specific transcripts.
• Comparison of intra- and inter-species genome sequence variation in orphan ORFs versus intergenic regions.

Main Results:

• A significant number of orphan ORFs were found to produce detectable transcripts and/or proteins.
• The naïve Bayes model, combined with transcript data, supported orphan ORFs as candidates for functional genes.
• Orphan ORFs exhibit lower sequence variation within species compared to intergenic regions, indicating functional constraint.
• Evidence suggests orphan ORFs are under selective pressure and resist deleterious mutations.

Conclusions:

• Orphan ORFs should not be solely removed from ORFeome annotation based on low inter-species sequence conservation.
• Multiple lines of evidence, including transcript and protein production, are necessary for accurate ORF evaluation.
• These under-conserved ORFs may play roles in micro-evolutionary divergence between yeast species.