The A and B lines of cantaloupe (Cucumis melo) were developed through a specific genetic modification to express a reduced accumulation of S-adenosylmethionine (SAM) and consequently the trait of delayed ripening. This was accomplished by the introduction of a bacteriophage encoded enzyme, S-adenosylmethionine hydrolase, capable of degrading and thus reducing SAM. The conversion of SAM to 1-aminocyclopropane-1-carboxylic acid (ACC) is the first step in ethylene biosynthesis and the lack of sufficient pools of SAM results in significantly reduced synthesis of this phytohormone, which is known to play a key role in fruit ripening.

These lines were created by Agrobacterium-mediated transformation in which the transfer-DNA (T-DNA) contained the S-adenosylmethionine hydrolase encoding SAMase gene from Escherichia coli bacteriophage T3. The constitutive expression of the SAMase gene was controlled by inclusion of regulatory DNA sequences from A. tumefaciens. In addition, the T-DNA contained sequences encoding the enzyme neomycin phosphotransferase II (NPTII) from the Tn5 transposon of Escherichia coli, strain K12, under the control of the nos promoter from A. tumefaciens. The expression of NPTII activity was used as a selectable trait to screen transformed plants for the presence of the SAMase gene.