Abstract
p-SINE1, a rice retroposon, is transcribed by RNA polymerase III (pol III). We have previously reported that the amount of p-SINE1 transcripts dramatically increased by treatment of cells with DNA-methylation inhibitors. We examined DNA methylation of a p-SINE1 member whose sequence is identical to the transcripts, and found that cytosine residues, not only in CpG sequences but also in CpHpG or CpHpH sequences, are methylated specifically in p-SINE1. The features of the p-SINE1 methylation were similar to those of RdDM (RNA-directed DNA methylation), induced by short interfering RNA (siRNA). To examine the involvement of siRNA in regulation of p-SINE1 expression, we performed northern blot analysis with RNA isolated from rice cells, and found siRNA which hybridized to the p-SINE1 sequence. The amount of the siRNA apparently decreased by the treatment with DNA-methylation inhibitors. These results suggest the possibility that siRNA is involved in regulation of the p-SINE1 expression.
