Regulation of the Enzyme UFGT by the Controlling Element Ds in bz-m4, an Unstable Mutant in Maize

Controlling, or transposable, elements in maize can transpose to practically any site in the maize genome (for recent reviews, see Fincham and Sastry 1974; Nevers and Saedler 1977). Genes that come under the control of transposable elements produce variegated or mosaic phenotypes consisting of normal-appearing sectors on an otherwise phenotypically mutant background. Such genes are sometimes referred to as unstable or mutable. The mutant phenotype in chimeric tissues results from the inhibition of gene action often caused by the association of a controlling element with a gene, whereas the normal sectors represent clones of cells in which the controlling element has transposed away from the gene, thus restoring expression of gene action.