Credit: Nucleic Acids Research Scientists at Tokyo Institute of Technology decipher how to quantitatively assess the effects of specific epigenetic changes on the rate of transcription by developing a mathematical model. For this, they successfully generated reconstituted chromatin bearing histone modifications in vitro. Their study published in Nucleic Acids Research provides an accurate quantitative approach for understanding how site-specific changes to histone proteins impact the accessibility of chromatin and gene expression levels. The creation of a single protein is a long and complicated process. Even just the generation of its blueprint itself, known as a coding transcript, from a DNA template involves numerous steps and players. To start with, the DNA is usually found neatly wrapped around proteins called histones to form a nucleosome, the fundamental subunit of a tightly condensed structure called chromatin. The extent of its condensation determines how much of the DNA is "available" for the transcription process. Changes to these histones, such as acetylation, also influence the accessibility of chromatin for gene expression. These "epigenetic" modifications play a crucial role in regulating gene expression. To date, much remains to be explored regarding how these epigenetic effects can be accurately quantified and how site-specific histone modifications can affect gene expression.