Paramutation's properties and puzzles.

Paramutation refers to the process by which homologous DNA sequences communicate in trans to establish meiotically heritable expression states. Although mechanisms are unknown, current data are consistent with the hypothesis that the establishment and heritable transmission of specific chromatin states underlies paramutation. Transcribed, noncoding tandem repeats and proteins implicated in RNA-directed transcriptional silencing in plants and yeast are required for paramutation, yet the specific molecules mediating heritable silencing remain to be determined.