In plants, MYC-related proteins function as transcription factors involved in anthocyanin production and trichome development. We cloned a gene, Atmyc1, and its corresponding cDNA, that encodes for a MYC-related protein from Arabidopsis thaliana. The putative protein has a basic/helix-loop-helix motif at the C-terminus and a highly homologous region with that of the maize B/R family at the N-terminus. The promoter region of Atmyc1 contains a Sph box (CATGCATG) that is known as a cis-regulatory element conferring seed-specific expression. In fact, Atmyc1 transcripts were more abundant in developing seeds than in stems and leaves where trichomes are normally expressed. Restriction fragment length polymorphism mapping demonstrated that Atmyc1 is located on the upper region of chromosome 4, which clearly indicates that Atmyc1 is distinct from the ttg (transparent testa glabrous) locus that affects both trichome development and anthocyanin biosynthesis.