<jats:p>The genes<jats:italic>hom</jats:italic>,<jats:italic>thrB</jats:italic>and<jats:italic>thrC</jats:italic>, encoding homoserine dehydrogenase, homoserine kinase (HK) and threonine synthase, respectively, involved in the last steps of threonine biosynthesis, have been studied in<jats:italic>Streptomyces</jats:italic>sp. NRRL 5331, the producer of the ethylene synthetase inhibitor aminoethoxyvinylglycine (AVG), in order to determine their role in the biosynthesis of AVG. Different null mutants were obtained by plasmid-mediated disruption of each of the three genes.<jats:italic>thrC</jats:italic>gene disruption had no effect on AVG production, while the disruption of<jats:italic>thrB</jats:italic>blocked HK activity and substantially reduced the yield of this metabolite, probably due to the accumulation of homoserine and/or methionine which have a negative effect on AVG biosynthesis. Disruption of<jats:italic>hom</jats:italic>(<jats:italic>thrA</jats:italic>) completely blocked AVG biosynthesis, indicating that homoserine lies at the branching point of the aspartic-acid-derived biosynthetic route that leads to AVG. The four carbon atoms of the vinylglycine moiety of AVG derive, therefore, from homoserine.