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All S-RNases in apple contained one intron at the same location within the hypervariable region. They code for 225-228 amino acids, however, the length of introns is variable and divided into three groups. The intron sequences of some S-RNases within the same group showed an extremely high similarity as well as their coding sequences, suggesting that they were generated from the same origin.
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Matsumoto et al. (2001) studied this question.
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