NOVELTY - A nucleotide leader sequence 5'-untranslated region (5'-UTR) comprises elements favorable to gene expression, such as repeated CAA trinucleotide elements in combination with repeated CT dinucleotide elements, is new.    USE - The sequence can be used for the biotechnological production of molecules; for the synthesis of recombinant proteins; for the synthesis of recombinant proteins intended to induce resistance to viral, bacterial, or fungal pathogens; for the synthesis of recombinant proteins intended to induce resistance to herbicides; for the synthesis of recombinant proteins intended to obtain a modified composition in fatty acids in the raw material and the products derived from it; for the synthesis of recombinant proteins intended to obtain a changed nutritional value of the raw material and the products derived from it; for the synthesis of recombinant proteins intended for the production of fuels, rubbers, and bioplastics; for the synthesis of industrial enzymes and commercial proteins; for the synthesis of pharmaceutical proteins; for the synthesis of oral or injectable vaccines for man or animals; for the synthesis of patient-specific injectable vaccines, preferably idiotype-specific, to be used in the treatment of tumors of the lymphatic system; for the synthesis of proteins involved in the production of secondary metabolites; and for the synthesis of proteins usable directly or indirectly as factors to identify and/or select transformed cells (all claimed).    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are: (1) a method of constructing inside plant expression vectors of 5'-UTRs in which the following elements are simultaneously present: Inr site of CaMV 35S, poly(CAA)n, octamer ACAATTAC, poly(CT)n, where n is greater than or equal to 2; (2) an amplification primer comprising a nucleotide sequence selected from the nucleotide sequences of fully defined 19-54 bp (SEQ ID NO. 2-7) given in the specification, or its complement; (3) natural leader sequences 5'-UTR possibly discovered, which appear insignificant variants, provided they are functionally similar, of the sequences above; (4) sequences deriving from mutations of the sequences above, which appear to generate insignificant variants, provided they are functionally similar, of the sequences above, where the mutations concern irrespectively deletions, insertions, transitions, or transversions of one or more nucleotides in the sequence; (5) a method for the artificial synthesis of the sequence comprises using the primers above; (6) bacterial strains carrying plasmids containing the sequence, selected from Escherichia coli, Agrobacterium tumefaciens, and Agrobacterium rhizogenes; (7) engineered virus strains containing the sequence; (8) plant cells transformed with expression vectors containing the sequence under the control of a constitutive promoter; (9) plants having the transient expression of any protein in which the RNA messenger contains the sequence above, where transient expression uses viral vectors, agroinfiltration, particle delivery, or electroporation; (10) dicotyledonous or monocotyledonous plants stably transformed with expression vectors containing the sequence above; and (11) progenies of dicotyledonous or monocotyledonous plants.