Abstract
BackgroundUpstream open reading frames (uORFs) are elements found in the 5'-region of an mRNA transcript, capable of regulating protein production of the largest, or major ORF (mORF), and impacting organismal development and growth in fungi, plants, and animals. In Drosophila, approximately 40% of transcripts contain upstream start codons (uAUGs) but there is little evidence that these are translated and affect their associated mORF.ResultsAnalyzing 19,389 Drosophila melanogaster transcript annotations and 666,153 dipteran EST sequences we have identified 44 putative conserved peptide uORFs (CPuORFs) in Drosophila melanogaster that show evidence of negative selection, and therefore are likely to be translated. Transcripts with CPuORFs constitute approximately 0.3% of the total number of transcripts, a similar frequency to the Arabidopsis genome, and have a mean length of 70 amino acids, much larger than the mean length of plant CPuORFs (40 amino acids). There is a statistically significant clustering of CPuORFs at cytological band 57 (p = 10-5), a phenomenon that has never been described for uORFs. Based on GO term and Interpro domain analyses, genes in the uORF dataset show a higher frequency of ORFs implicated in mitochondrial import than the genome-wide frequency (p < 0.01) as well as methyltransferases (p < 0.02).ConclusionBased on these data, it is clear that Drosophila contain putative CPuORFs at frequencies similar to those found in plants. They are distinguished, however, by the type of mORF they tend to associate with, Drosophila CPuORFs preferentially occurring in transcripts encoding mitochondrial proteins and methyltransferases. This provides a basis for the study of CPuORFs and their putative regulatory role in mitochondrial function and disease.
Highlights
Upstream open reading frames are elements found in the 5'-region of an mRNA transcript, capable of regulating protein production of the largest, or major ORF, and impacting organismal development and growth in fungi, plants, and animals
13,746 contain unique Flybase gene numbers, 5,851 of which contain one or more AUGs upstream of the major ORF (mORF). This suggests that 43% of Drosophila mORF proteins could be affected in their expression level by translated Upstream open reading frames (uORFs)
A Drosophila gene coding for a putative mannosyl transferase contains a uORF-mORF pair that seems to be evolutionarily conserved in insects [19]
Summary
Upstream open reading frames (uORFs) are elements found in the 5'-region of an mRNA transcript, capable of regulating protein production of the largest, or major ORF (mORF), and impacting organismal development and growth in fungi, plants, and animals. In Drosophila, approximately 40% of transcripts contain upstream start codons (uAUGs) but there is little evidence that these are translated and affect their associated mORF. Upstream start codons (uAUGs), AUGs found 5' of the longest, or major, open reading frame (mORF), occur in 20–50% of eukaryotic mRNAs of a given genome [1,2,3,4,5]. The yeast General Control Nondepressible 4 (GCN4) transcript contains multiple uORFs that differentially regulate the protein level of a transcription factor-encoding mORF under starvation and non-starvation conditions. Oncogenes Mdm2 [12], her-2 [13], MYEOV [14], Bcl-2 [15], and SCL [16], all contain uORFs that affect the level of oncoproteins produced
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