As chromatin is condensed into the primary nucleosome structure, DNA becomes less accessible for transcription factors. With the loosening of this chromatin structure, however, transcription machinery is better able to access the genomic DNA, and transcription is thus promoted.
Does chromatin reduce transcription?
Thus the extent of compaction of the chromatin in the different states will affect the ability of transcription factors, polymerases, repair enzymes, and the recombination machinery to access this substrate. More open, accessible chromatin is associated with greater transcriptional activity.
What is the role of chromatin in transcriptional regulation?
In eukaryotes, the tight or loose packaging of the genes in chromatin (DNA plus specific proteins) can control whether the genes can be expressed to form their encoded product. Chromatin is usually not “permissive” but it can be modified in specific areas to open it up for transcription of the genes.
What happens to chromatin during transcription?
Chromatin structure imposes significant obstacles on all aspects of transcription that are mediated by RNA polymerase II. The dynamics of chromatin structure are tightly regulated through multiple mechanisms including histone modification, chromatin remodeling, histone variant incorporation, and histone eviction.
Does chromatin structure change during transcription?
Transcription or replication may alter chromatin structure during synthesis, enabling regulatory factor binding and, potentially, future rounds of transcription.
Which type of chromatin supports transcription of mRNA?
Functions of euchromatin
Euchromatin is the part of the chromatin involved in the active transcription of DNA into mRNA. As euchromatin is more open in order to allow the recruitment of RNA polymerase complexes and gene regulatory proteins, so transcription can be initiated.
How are chromatin modifications passed down?
However, during DNA replication, the parental histone proteins are all removed from the DNA during the process of chromatin disassembly, and the chromatin is reassembled onto the two daughter DNA duplexes following DNA replication.
What happens to histones during transcription?
At the same time, during intense transcription histones are largely removed from DNA in vivo. Under these circumstances, histone-free DNA could be available for binding to the transiently exposed octamer surface, and translocation of the nucleosomes remaining on the genes would become much more likely.
Which type of chromatin is transcriptionally inactive?
The two types of chromatin, heterochromatin and euchromatin, are functionally and structurally distinct regions of the genome. Heterochromatin is densely packed and inaccessible to transcription factors so it is rendered transcriptionally silent (Richards and Elgin 2002).
Does chromatin have RNA?
Whether RNA itself plays a direct structural role in chromatin is, however, not known. Here, we report results indicating that RNA plays a general structural role in eukaryotic chromatin. Our results indicate that purified chromatin contains significant amounts of RNA (2%–5% of total nucleic acids).