Apple Allergy: The cDNA Sequence of the Major Allergen of Apple, Determined by Performing PCR with a Primer Based on the N-Terminal Amino Acid Sequence, is Highly Homologous to the Sequence of the Major Birch Pollen Allergen

Considering the known N‐terminal amino acid sequence of the major apple allergen, a polymerase chain reaction (PCR) primer was selected to amplify cDNA encoding this protein. A single PCR product was obtained, cloned into Escherichia coli and subsequently sequenced. The missing 5′‐end of the apple cDNA sequence was obtained by a 5′‐RACE method. The cDNA sequence showed 72% identity with the coding region of one of the known isoforms of Bet v 1, the major allergen of birch pollen. The deduced amino acid sequence resulted in a 158‐residue protein with a calculated molecular mass of 17·5 kDa and 63% amino acid sequence identity to Bet v 1. In addition, further protein alignments showed a high degree of identity with allergens from other tree pollens and some ‘pathogenesis‐related proteins’ from food plants. According to international regulations the allergen was termed Mal d 1 for this protein, it being the first major allergen discovered and characterised in fruits of apple (Malus domestica).