Disclosed is an Artificial DNA sequence of a 5'-UTR leader region (containing one or more copies of the octamer ACAATTAC) effective in enhancing the expression of heterologous proteins in plants, and having elements favourable to gene expression in plants, comprising at least a poly(CAA) region, meaning an oligonucleotide consisting of two or more copies of the CAA element contiguous with each other in combination with at least a poly(CT) region, meaning an oligonucleotide consisting of two or more copies of the CT element contiguous with each other. Further disclosed are bacterial strains and engineered virus strains containing said sequence, and plant cells and plants transformed with expression vectors containing said sequence.
