Transcriptional, post-transcriptional, translational and post-translational
Expansion
Transcriptional (the principal level)
- Promoters and enhancers bound by transcription factors
- Chromatin structure: DNA wrapped tightly on histones is inaccessible
- Epigenetic modification: DNA methylation at CpG islands silences genes; histone acetylation opens chromatin and activates them
Post-transcriptional: alternative splicing, allowing one gene to make many proteins; RNA stability; microRNA silencing.
Translational: initiation factor availability, iron response elements.
Post-translational: phosphorylation, glycosylation, cleavage, and targeted degradation by the ubiquitin-proteasome system.
Epigenetics in medicine: genomic imprinting explains why Prader-Willi and Angelman syndromes arise from the same chromosomal region depending on the parent of origin; X inactivation explains mosaicism in female carriers of X-linked disease; and hypermethylation silencing tumour suppressor genes is a common step in carcinogenesis, which is the rationale for demethylating agents in myelodysplasia.