Résumé
The carriers of epigenetic information are chromosomal (DNA, histones and other associated proteins) and extrachromosomal (regulatory RNAs). These carriers undergo specific molecular modifications and are found at precise locations in the genome. This chapter discusses a panoply of very precise epigenetic mechanisms involving a great specificity of carriers, players and deposited marks. Epigenetic marks are dynamically positioned along chromosomes, influencing chromatin compaction and topology. These epigenetic marks represent signals that appear to be indispensable to various genome functions. Epigenetic marks also ensure the adaptation of organisms to environmental stress, thus enabling their survival, and they can even be transmitted across generations, thus contributing to a form of epigenetic heredity. In addition to these various epigenetic mechanisms, there are post‐transcriptional modifications at the RNA level (known as “epitranscriptomic modifications”), such as methylations observed in tRNAs, rRNAs and even messenger RNAs.