Maintenance DNA methyltransferase (Met1) and silencing of CpG-methylated foreign DNA in Volvox carteri.
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-methylated 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.
Babinger
P
P
Institute for Biochemistry, Genetics and Microbiology, University of Regensburg, 93040 Regensburg, Germany. patrick.babinger@biologie.uni-r.de
Völkl
R
R
Cakstina
I
I
Maftei
A
A
Schmitt
R
R
D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D002455:Cell Division; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D018899:CpG Islands; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000235:genetics* / Q000378:metabolism*; D004261:DNA Replication; D004251:DNA Transposable Elements / Q000235:genetics; D048028:DNA, Algal / Q000235:genetics / Q000378:metabolism; D020868:Gene Silencing; D008969:Molecular Sequence Data; D044446:Volvox / Q000201:enzymology* / Q000235:genetics*
D020418:Algal Proteins; D004251:DNA Transposable Elements; D048028:DNA, Algal; D015254:DNA Modification Methylases