Researchers have implicated RNA in epigenetic heredity, according to a report in this week's Nature. RNA polymerase, say the authors, is an essential part of a process in which interactions between two parental alleles influence offspring expression.Some researchers have suspected that this process, known as paramutation, may involve RNA, said Ting Wu of Harvard Medical School, who was not involved in the study, but "the critical link that [this group has] been able to put through has been lacking." Led by Mary Alleman of Duquesne University in Pittsburgh, the researchers examined paramutation at the b1 gene in maize, which determines whether a plant's stalk is purple or green. If a plant possesses the dominant allele B-I, its stalk is normally purple. However, if the other chromosome contains the paramutagenic allele B', then B-I's expression is silenced, and the plant appears green. Once B-I expression has...

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