A novel approach to gene discovery and analysis is described. A small exon flanked by consensus 3' and 5' splice sites was synthesized. The exon contains open reading frames encoding 43 amino acid peptides. There are no stop codons in any of the three reading frames, and each reading frame contains an epitope recognized by the same monoclonal antibody. The exon can be inserted into the introns of genes, and the resulting small peptide will be incorporated into the protein encoded by the host gene, regardless of the class of intron. The protein can then be recognized by the antibody, permitting functional studies.