Methylcinnamate is an aromatic compound with a cinnamon flavor that is widely distributed throughout the plant kingdom. This compound may serve as a signaling molecule between plants and insects. The gene product responsible for catalyzing the last step in the biosynthesis of methylcinnamate has remained unidentified until now. We created an EST database using a cDNA library created from the glandular trichomes of a methylcinnamate-producing variety of basil (line MC) as well as libraries from basil lines producing little to no methylcinnamate. Within this database we identified a gene with homology to other members of the plant carboxyl methyltransferase gene family that was highly and almost exclusively expressed in line MC. Subsequent expression profiling and enzyme activity assays correlated a glandular trichome-specific expression pattern and specific enzymatic activity for this carboxyl methyltransferase, which we have named cinnamate carboxyl methyltransferase (CACMT). We have also expressed the cDNA encoding basil CACMT in E. coli and confirmed the biochemical activity of the gene product. Structural modeling of the CACMT protein based on the solved crystal structure of Clarkia SAMT (salicylic acid carboxyl methyltransferases) revealed active site modifications that may be responsible for the substrate preference of CACMT. We have proposed residues for site-directed mutagenesis that have the potential to alter the enzyme activity to that of SAMT and are currently in the process of experimentally testing the effects of the proposed changes on catalysis and enzyme function.