Exon shuffling in anther-specific genes from sunflower.

We describe here the nucleotide sequence of an anther-specific gene (sf18) from sunflower, encoding a proline- and glycine-rich polypeptide with a hydrophobic amino-terminus (signal peptide). The gene is split by a 211 bp intron and is partially related to another anther-specific gene (sf2) from sunflower with which it shares important sequence stretches in the 5' coding and upstream regions. We propose that the two gene have originated via exon shuffling, during which a copy of a DNA segment including the promoter region as well as a signal peptide coding sequence has been transferred into the upstream region of two different potential coding sequences, generating two novel genes which display the same specificity of expression and which both encode an extracellular protein. While the 5' region of the intron is highly conserved as part of the transferred region and may play a role in the selection of the 5' splice site, a common octanucleotide at the 3' end of the intron of the two genes might be involved in 3' splice site selection.