the present invention provides an isolated dna sequence which encodes at least part of the tomato enzyme endopolygalacturonase pg1 beta - subunit . this dna sequence preferably encodes a polypeptide , the n - terminal amino acid sequence of which is : e - k - h - s - g - d - i - h . in other preferred forms of the invention the dna sequence encodes a polypeptide which includes one of the following amino acid sequences : e - k - h - s - g or n - y - g - q - x - f - n - e - g . the dna sequence of the present invention may be used to produce genetically engineered tomato plants with modified ripening characteristics .