The amino acid methionine is a common protein building block that is also important in other cellularprocesses. Plants, unlike animals, synthesize methionine de novo and are thus a dietary source of thisnutrient. A new approach for using maize as a source of nutrient methionine is described. Maize seeds, amajor component of animal feeds, have variable levels of protein-bound methionine. This variability is aresult of post-transcriptional regulation of the Dzs10 gene, which encodes a seed-speci®c highmethioninestorage protein. Here we eliminate methionine variability by identifying and replacing thecis-acting site for Dzs10 regulation using transgenic seeds. Interestingly, two different mechanisms affectmRNA accumulation, one dependent on and the other independent of the untranslated regions (UTRs) ofDzs10 RNA. Accumulation of chimeric Dzs10 mRNA was not reduced in hybrid crosses and wasuncoupled from genomic imprinting by Dzr1, a regulator of Dzs10. Uniform high levels of Dzs10 proteinwere maintained over ®ve backcross generations of the transgene. The increased level of methionine inthese transgenic seeds allowed the formulation of a useful animal feed ration without the addition ofsynthetic methionine.