PROBLEM TO BE SOLVED: To provide a paraxanthine N-methyltransferase derived from coffee, DNA or RNA encoding the enzyme, a microorganism and a plant transformed with the DNA and to provide a method for changing caffeine amount or the amount of its precursor by a nucleic acid structure containing the RNA by using the plant or its cultured cell or tissue. SOLUTION: The enzyme is produced by a microorganism or a plant body or its cultured cell transformed with a vector containing DNA or RNA and encoding a polypeptide having enzyme activity of paraxanthine N-methyltransferase or the expression amount of the enzyme is suppressed by an antisense RNA. According to the present invention, the paraxanthine N-methyltransferase utilizable as an enzyme for industrial, food or medical application can efficiently be produced. According to the present invention, a formation ratio of a caffeine metabolic compound group can be modified by modifying a caffeine biosynthesis metabolism of a caffeine-producing plant, plant tissue or plant cell. COPYRIGHT: (C)2004,JPO
