Final answer:
Regions of a protein responsible for binding to nucleosomes with posttranslational modifications (PTMs) are known as reader domains. These domains play a pivotal role in interpreting the epigenetic state of chromatin and influence gene expression by altering the accessibility of DNA for transcription.
Step-by-step explanation:
Regions of a protein that control the binding of particular proteins to nucleosomes with posttranslational modifications (PTMs) are called reader domains. These domains are integral to the regulation of gene expression, playing a critical role by interpreting the epigenetic marks on histone proteins and DNA. The interaction between reader domains and nucleosomes can influence the accessibility of the DNA to transcriptional machinery, thereby affecting gene expression. These domains hence act as intermediaries, recognizing and binding to specific PTMs on nucleosomes, such as methyl, acetyl, or phosphate groups, which can convert the chromosomal region from an open to a closed state or vice versa, allowing or restricting transcription.
These modifications do not change the DNA sequence but instead affect the physical structure of chromatin, which in turn influences gene expression. Epigenetic regulation via reader domains is a key mechanism in cellular responses to environmental stimuli and during developmental processes.