Paramutation of the r1 locus of maize is associated with increased cytosine methylation.
In paramutation two alleles of a gene interact so that one of the alleles is epigenetically silenced. The silenced state is then genetically transmissible for many generations. The large (220 kbp) multigenic complex R-r is paramutable: its level of expression is changed during paramutation. R-r was found to exhibit increases in its level of cytosine methylation (C-methylation) following paramutation. These C-methylation changes are localized to the 5' portions of the two genes in the complex that are most sensitive to paramutation. These methylation changes flank a small region called sigma that is thought to have been derived from a transposon named doppia. A mutant derivative of R-r that has a deletion of the sigma region fails to become methylated under conditions in which R-r is heavily methylated. This suggests that the presence of sigma sequences at the locus is required for the methylation changes that are observed following paramutation.
Walker
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Biology Department, University of Massachusetts, Amherst 01003, USA. ewalker@bio.umass.edu
D002874:Chromosome Mapping; D003596:Cytosine / Q000378:metabolism*; D019175:DNA Methylation; D017343:Genes, Plant; D018257:Helix-Loop-Helix Motifs; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics*; D010940:Plant Proteins / Q000235:genetics*; D017384:Sequence Deletion; D003313:Zea mays / Q000235:genetics*
D009687:Nuclear Proteins; D010940:Plant Proteins; C085200:R protein, Zea mays; D003596:Cytosine