TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Nucleotide Sequence: The sequence contains a poly(CAA) region (an oligonucleotide comprising two or more copies of the CAA element, preferably but not necessarily contiguous with each other). It also contains a poly(CT) region (an oligonucleotide consisting of two or more copies of the CT element, preferably but not necessarily contiguous with each other). The sequence contains one or more copies of the octamer ACAATTAC. The sequence comprises any combination of the sequences above. The sequence comprises a combination of the sequences above with the Inr site of CaMV 35 S, that is, the transcription initiation site of the cauliflower mosaic virus 35S promoter. Preferably, the sequence comprises fully defined 73 bp (SEQ ID NO. 1) given in the specification. The sequence also comprises all the possible combinations of the elements that constitute the leader sequence 5'-UTR, irrespective of their relative positioning 5 '-3'. It also comprises sequences complementary to the sequences above. The sequence has a length of 20-200 nucleotides, preferably 40-150 nucleotides. The sequence has a G+C content of less than 60%, preferably less than 50%. The sequence is obtainable from artificial synthesis; or natural or induced processes of recombination inside natural or artificial sequences. Preferred Plant Cells: The plant cells are transformed with expression vectors containing the sequence under the control of a tissue-specific promoter such as a seed-specific promoter. It is also under the control of an inducible promoter. The plant cells are transformed with expression vectors containing the sequence under the control of a promoter with phase-dependent transcriptional activity, under the control of a promoter active in the chloroplast, or under the control of a promoter active in the mitochondrion. Preferred Plants: The plants comprise one or more species belonging to the families Solanaceae, Papilonaceae, Cruciferae, and Graminaceae (Poaceae). ACTIVITY - Cytostatic. No biological data given.    MECHANISM OF ACTION - Vaccine.    ADMINISTRATION - Administration is by oral and injection (all claimed). No dosage details given.    SPECIFIC SEQUENCES - Specifically claimed is nucleotide leader sequence 5'-UTR comprising 73 bp (SEQ ID NO. 1), and amplification primers comprising 19-54 bp (SEQ ID NO. 2-7). All sequences are fully defined in the specification. cacccggggatcctctaga (SEQ ID NO. 7)    EXAMPLE - No example given.