Chromosomal elements conferring epigenetic inheritance

Epigenetic regulation of transcription can lead to a stable differential ex pression of identical genetic information in the same cell or cell populati on. There is increasing evidence that higher order chromatin structures, in volving specific multiprotein complexes, constitute one device to establish and maintain epigenetic marks. In addition, defined chromosomal elements c onferring epigenetic inheritance of transcriptional expression states have recently been identified. During the period where the difference in express ion of identical genes is established, these sequences appear to be used as switch elements by both negative and positive regulators. Once the epigene tic mark is "set", the elements maintain either the silenced or the activat ed expression state over many cell generations. Here we review recent data obtained from analyzing epigenetic gene regulation in different organisms a nd show that similarities in the underlying mechanisms appear to exist. Bio Essays 21:824-832, 1999. (C) 1999 John Wiley & Sons, Inc.