Restriction endonuclease fragments containing part of the Waxy (Wx) locus have been cloned from strains with insertion mutations at the locus caused by the controlling elements Activator (Ac) and Dissociation (Ds). Evidence is presented that the genetically defined Ac element corresponds to a 4.3 kb insertion, while the two Ds elements correspond to 4.1 kb and 2.0 kb insertions, all near the 3' end of the Wx transcription unit. The 4.1 kb Ds is almost completely homologous to the Ac element, differing by a central deletion of less than 0.2 kb. The 2.0 kb Ds element is homologous to the ends of the Ac element. Sequences homologous to the ends of the Ac element are present in many copies in the genomes examined, while there are ten or fewer copies of a sequence with homology to the center of the cloned Ac element. The Ac element at the Wx locus can be distinguished structurally from the other Ac-like sequences in the genome.