Phylogenetically widespread alternative splicing at unusual GYNGYN donors
1 Institute of Computer Science, Chair for Bioinformatics, Albert-Ludwigs-University Freiburg, Georges-Koehler-Allee 106, 79110 Freiburg, Germany
2 Genome Analysis, Leibniz Institute for Age Research - Fritz Lipmann Institute, Beutenbergstr. 11, 07745 Jena, Germany
3 Institute of Clinical Molecular Biology, Christian-Albrechts-University Kiel, Schittenhelmstr. 12, 24105 Kiel, Germany
4 Max Planck Institute for Molecular Genetics, Ihnestr. 63, 14195 Berlin, Germany
Genome Biology 2006, 7:R65 doi:10.1186/gb-2006-7-7-r65Published: 25 July 2006
Splice donor sites have a highly conserved GT or GC dinucleotide and an extended intronic consensus sequence GTRAGT that reflects the sequence complementarity to the U1 snRNA. Here, we focus on unusual donor sites with the motif GYNGYN (Y stands for C or T; N stands for A, C, G, or T).
While only one GY functions as a splice donor for the majority of these splice sites in human, we provide computational and experimental evidence that 110 (1.3%) allow alternative splicing at both GY donors. The resulting splice forms differ in only three nucleotides, which results mostly in the insertion/deletion of one amino acid. However, we also report the insertion of a stop codon in four cases. Investigating what distinguishes alternatively from not alternatively spliced GYNGYN donors, we found differences in the binding to U1 snRNA, a strong correlation between U1 snRNA binding strength and the preferred donor, over-represented sequence motifs in the adjacent introns, and a higher conservation of the exonic and intronic flanks between human and mouse. Extending our genome-wide analysis to seven other eukaryotic species, we found alternatively spliced GYNGYN donors in all species from mouse to Caenorhabditis elegans and even in Arabidopsis thaliana. Experimental verification of a conserved GTAGTT donor of the STAT3 gene in human and mouse reveals a remarkably similar ratio of alternatively spliced transcripts in both species.
In contrast to alternative splicing in general, GYNGYN donors in addition to NAGNAG acceptors enable subtle protein variations.