Sporamin, the major soluble protein of sweet potato tuberous roots (
Ipomoea batatas
), has a relatively balanced aminoacid content, but it is limited in lysine and methionine. A 240 base pair DNA fragment was designed and synthesized in order to improve the aminoacidic quality of the sporamin. From a total DNA preparation and using polimerase chain reaction, the region containing the sporamin gene and its regulatory regions was amplified. The DNA obtained was cloned and sequenced. Besides, we amplified by PCR a fragment containing the sporamin gene, the sequences coding for transit to vacuoles and the signal peptides. This region was cloned, sequenced and expressed in Escherichia coli. With the use of specific restriction endonucleases, two strategies were developed to insert the DNA synthetic fragment in two different positions of the structural gene for sporamin. Predictions of the possible features of the modified sporamins were performed using appropriate softwares. The genetic variants obtained were checked by restriction, hibridization and sequencing. Their expression in E. coli was detected by Western blotting.