Regulation of activator/dissociation transposition by replication and DNA methylation.
In maize the transposable elements Activator/Dissociation (Ac/Ds) transpose shortly after replication from one of the two resulting chromatids ("chromatid selectivity"). A model has been suggested that explains this phenomenon as a consequence of different affinity for Ac transposase binding to holo-, hemi-, and unmethylated transposon ends. Here we demonstrate that in petunia cells a holomethylated Ds is unable to excise from a nonreplicating vector and that replication restores excision. A Ds element hemi-methylated on one DNA strand transposes in the absence of replication, whereas hemi-methylation of the complementary strand causes a >6.3-fold inhibition of Ds excision. Consistently in the active hemi-methylated state, the Ds ends have a high binding affinity for the transposase, whereas binding to inactive ends is strongly reduced. These results provide strong evidence for the above-mentioned model. Moreover, in the absence of DNA methylation, replication enhances Ds transposition in petunia protoplasts >8-fold and promotes formation of a predominant excision footprint. Accordingly, replication also has a methylation-independent regulatory effect on transposition.
Ros
F
F
Institut für Genetik und Mikrobiologie, Universität München, 80638 Munich, Germany.
Kunze
R
R
D004249:DNA Damage; D018983:DNA Footprinting; D019175:DNA Methylation; D004261:DNA Replication; D004251:DNA Transposable Elements; D018744:DNA, Plant; D019895:Transposases; D003313:Zea mays / Q000235:genetics*
D004251:DNA Transposable Elements; D018744:DNA, Plant; D019895:Transposases