Abstract
DNA methylation plays an important role in the gene-silencing network of higher eukaryotes. We have analyzed the 21.5-kb maintenance methyltransferase (M-MTase) gene, met1, of the multicellular green alga Volvox carteri. The met1 transcript was detected only during the period when DNA replication and cell division are taking place. It encodes a 238 kDa protein containing eight C-terminal activity domains typical of M-MTases, plus upstream DNA-binding domains including the ProDom domain PD003757, which experimental analyses in animal systems have indicated is required for targeting the enzyme to DNA-replication foci. Several insertions of unknown function make Volvox Met1 the largest known member of the Met1/Dnmt1 family. Here we also show that several endogenous transposon families are CpG-methyated in Volvox, which we think causes them to be inactive. This view is supported by the observation that an in vitro CpG-methylated gene introduced into Volvox was maintained in the methylated and silent state over >100 generations. Thus, we believe that Met1 recognizes and perpetuates the in vitro methylation signal, and that the silencing machinery is then able to transduce such a methylation-only signal into a stable heterochromatic (and silent) state.
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Acknowledgments
This work was supported by Deutsche Forschungsgemeinschaft (SFB 521/B1). We thank Manuela De Lazzer for technical help and David Kirk for critical review of the manuscript.
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Babinger, P., Völkl, R., Cakstina, I. et al. Maintenance DNA methyltransferase (Met1) and silencing of CpG-methylated foreign DNA in Volvox carteri . Plant Mol Biol 63, 325–336 (2007). https://doi.org/10.1007/s11103-006-9091-1
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DOI: https://doi.org/10.1007/s11103-006-9091-1