SINE retroposons can be used in vivo as nucleation centers for de novo methylation

SINEs (short interspersed elements) are an abundant class of transposable e lements found in a,vide variety of eukaryotes. Using the genomic sequencing technique, we observed that plant S1 SINE retroposons mainly integrate in hypomethylated DNA regions and are targeted by methylases. Methylation can then spread from the SME into flanking genomic sequences, creating distal e pigenetic modifications. This methylation spreading is vectorially directed upstream or downstream of the S1 element, suggesting that it could be faci litated when a potentially good methylatable sequence is single stranded du ring DNA replication, particularly when located on the lagging strand. Repl ication of a short methylated DNA region could thus lead to the de novo met hylation of upstream or downstream adjacent sequences.