The field of epigenetics has expanded rapidly in recent years thanks to the identification and characterization of the biochemical processes that are associated with distinct chromatin states. The fascinating complexity of the enzymes that deposit and remove histone modifications, as well as the factors that bind to these modifications, has been at the forefront of epigenetics research. Methylation, a kind of histone modification, is essential for the regulation of transcription, genome integrity and epigenetic inheritance. The recent discovery of enzymes that antagonize or remove this modification suggests that, contrary to previous notions, histone methylation is dynamically regulated, as discussed on page 307 by Robert J. Klose and Yi Zhang and in the Research Highlight on page 270.

The Review by Kenneth K. Lee and Jerry L. Workman (page 284) features the cellular machinery that has a role in a different type of histone modification, acetylation. Histone acetyltransferases have diverse functions, and they modify histone as well as non-histone substrates.

In fact, p53, the best-characterized non-histone substrate, is the subject of this month's article in the Series on Mechanisms of disease. Although the function of p53 as a tumour suppressor means that we can't live without it, an integrated view of p53 functions suggests that not all of its functions are conducive to a long and healthy life. Karen H. Vousden and David P. Lane (page 275) review recent studies that challenge the view that p53 just protects us from cancer. Instead, p53 seems to have important roles in development and might contribute to a number of disease aetiologies.

Last, this month also sees the introduction of a new article type in the journal — Analysis (page 319; for more information, see the author guidelines on our website).