Transposase activity of the Ac controlling element in maize is regulated by its degree of methylation

Abstract

The maize controlling element activator, Ac, is capable of self-transposition. We isolated a spontaneously arisen derivative, (wx-m9Ds-cy) of the Ac element present in the wx-m9Ac mutant which does not itself transpose but can be induced to transpose by the presence of an Ac element elsewhere in the genome. The wx-m9Ds-cy derivative reverts to an active Ac form. A comparison of cloned isolates of the three forms of the element shows no differences in restriction enzyme pattern. Southern analysis of the genome organization of the elements shows marked differences in the methylation pattern. The active Ac element is methylated at one end of the element while the inactive derivative wx-m9Ds-cy is completely methylated at all HpaII sites in the element. The revertant Ac is partially demethylated. Reversion of the mutants to the active form appears to be at least a two-step process.