Recombinant DNA techniques; SYNTHETIC GEN; PROCESS FOR THE PREPARATION THEREOF; Plasmid vector; PROCESS FOR THE PREPARATION THEREOF; CELL; Method for transforming a cell; Process for the experimentation of a peptide; THUS OBTAINED Peptide; (Aspartyl-phenylalanine) N; PROCESS FOR THE PREPARATION OF aspartyl-phenylalanine methyl ester; THUS OBTAINED aspartyl-phenylalanine methyl ester; PROCESS FOR THE PREPARATION OF L-phenylalanine or L-aspartic acid.