Transposase binding site methylation in the epigenetically inactivated Ac derivative Ds-cy

The authors have determined the C-methylation pattern of the non-autonomous transposable element Ds-cy, which is an epigenetically inactivated, transcriptionally silent derivative of the maize Activator (Ac) element. Like Ac, Ds-cy is hypermethylated at the 3-end. However, in Ds-cy the 5-end is also hypermethylated, including all subterminal binding sites for the Ac-encoded transposase protein. As Ds-cy transposes in the presence of an active Ac in the genome, the authors conclude that methylation of the 5-end TPase binding sites does not interfere with transposition, but correlates with inactivity of the Ac promoter. the authors discuss the implications of these results for the chromatid selectivity of Ac/Ds transposition and the mechanism of Ac-induced chromosome breakage events.