DNA methylation of maize transposable elements is correlated with activity.
Transposition of the maize transposable elements Ac, Spm and Mu is correlated with a lack of methylation. For both Ac (Schwartz & Dennis 1986) and Spm (Fedoroff et al. 1988) methylation of a region upstream and downstream of the site of initiation of transcription results in a loss both of mRNA encoding for the transposase and the ability to excise. We have studied the activation of an inactive, methylated derivative of Ac by using a cycle of tissue culture. A passage through tissue culture results in activation of the element and is correlated with demethylation of the 5' end of the transposase gene. Demethylation and activation may occur as a multistep process. We propose a model in which binding of the Ac transposase to the 5' region of the Ac element prevents methylation following replication. Consequently, demethylation and reactivation occurs.
Dennis
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CSIRO Division of Plant Industry, Canberra, ACT, Australia.
Brettell
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RI
D000483:Alleles; D004247:DNA / Q000235:genetics* / Q000378:metabolism; D004251:DNA Transposable Elements; D008745:Methylation; D010944:Plants / Q000235:genetics*; D015183:Restriction Mapping; D003313:Zea mays / Q000235:genetics*
D004251:DNA Transposable Elements; D004247:DNA