The maize C1 gene is a regulatory gene of the anthocyanin pathway. It is a part of a multigene family whose predicted protein products contain a region with homology to the DNA-binding domain of myb proto-oncogene products. Using as a probe an oligonucleotide mixture encoding a highly conserved region in plant MYB proteins, cDNAs encoding three related polypeptides expressed in the flower of Petunia hybrida have been isolated. Predicted proteins are 280-517 amino acids long and show sequence similarities among themselves as well as with other MYB proteins (45-80% amino acid identity) in the MYB DNA-binding domain. Outside this domain no significant sequence similarity was found. However, in all cases regions with structural characteristics of activator domains were found. Analysis with Southern blots allowed an estimation of at least 20-30 myb genes in P. hybrida. Expression patterns were specific for each gene as shown by Northern blotting analysis. Subcellular location studies of the largest MYB product, by both immunoblotting of the protein in subcellular fractions and by 'in situ' immunolocation experiments, showed that it is a nuclear protein. The role of MYB proteins as transcriptional activators regulating the synthesis of different anthocyanin(flavonoid)-related compounds is discussed.