The structure of the wild-type c1 locus of Zea mays was determined by sequence analysis of one genomic and two cDNA clones. The coding region is composed of three exons (150 bp, 129 bp and one, at least 720 bp) and two small introns (88 bp and 145 bp). Transcription of the mRNAs corresponding to the two cDNA clones cLC6 (1.1 kb) and cLC28 (2.1 kb) starts from the same promoter. Both cDNAs are identical except that cLC28 extends further at its 3' end. A putative protein, 273 amino acids in length was deduced from the sequence of both transcripts. It contains two domains, one basic and the other acidic and might function as a transcriptional activator. The basic domain of this c1-encoded protein shows 40% sequence homology to the protein products of animal myb proto-oncogenes.