Two maize genes, Zm 1 and Zm 38, related to the regulatory anthocyanin gene C1 were analyzed molecularly and used for fusion constructs in transient domain swapping experiments with the C1 wild-type gene. It was shown that both genes (Zm 1 and Zm 38) influence the expression of the A1 locus, a target gene for C1. Zm 1 activates the A1 promoter, however it does not turn on the whole anthocyanin pathway. The Zm 38 gene product shows functions similar to C1-I, a dominant inhibitor of the C1 wild-type gene. Concerning the trans-inhibition by C1-I two effects seem to be involved, competition for binding and formation of heterodimers. Further analysis of C1 function was carried out by a fine structure analysis of C1 mutants induced by the insertion and excision of transposable elements. These experiments indicate that for the activating domain of the protein, the formation of an alpha helix seems to be more important than a high negative charge.