TRANSPOSASE BINDING-SITE METHYLATION IN THE EPIGENETICALLY INACTIVATED AC DERIVATIVE DS-CY

The authors have determined the C-methylation pattern of the non-auton omous transposable element Ds-cy, which is an epigenetically inactivat ed, transcriptionally silent derivative of the maize Activator (Ac) el ement. Like Ac, Ds-cy is hypermethylated at the 3'-end. However, in Ds -cy the 5'-end is also hypermethylated, including all subterminal bind ing sites for the Ac-encoded transposase protein. As Ds-cy transposes in the presence of an active Ac in the genome, the authors conclude th at methylation of the 5'-end TPase binding sites does not interfere wi th transposition, but correlates with inactivity of the Ac promoter. T he authors discuss the implications of these results for the chromatid selectivity of Ac/Ds transposition and the mechanism of Ac-induced ch romosome breakage events.