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Theory of Intelligent Design, the best explanation of Origins » Origin of life » Protein Complexes Help Form 3D shape of Chromatin

Protein Complexes Help Form 3D shape of Chromatin

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Protein Complexes Help Form 3D shape of Chromatin 1

Loops help regulate transcription from DNA to messenger RNA. A vast library of protein complexes, making a large number of different shapes, aids the formation of loops. These proteins, also, help to fix the chromatin in particular parts of the nucleus. Three large complexes especially help make 3D chromatin shapes–CTCF, cohesion and Mediator.

The insulator protein CTCF holds together long-range interactions of different sections of the chromatin near the TADs. In fact, these CTCF loops help create the basic structure of the TADs. Some CTCFs are insulators, that is, they keep long-range sections of chromatin apart. But, others don’t.

CTCF has many functions. 2CTCF forms insulators, that is, regions of DNA that are blocked by “insulating” the interaction of enhancers and promoters. Also, CTCF binds the loops to the nuclear lamina determining 3D localization in the nucleus. CTCF forms a boundary between active and inactive types of chromatin. All of these allow CTCF to influence the types of genetic networks that are used in that type of cell. One

Another protein complex that alters shape is the cohesion complex. Cohesins create loops related to enhancers, different in each type of cell. They are also constitutive. They form a ring holding together the chromatids after they are copied. Cohesins connect chromatin during cell division. They attach spindles to chromosomes and help recombination of regions of DNA during division (a key to evolution) and for repair of broken DNA. It, also, regulates transcription.



MediatorA third critical protein complex is Mediator (Noble Prize in 2006 was given for this critical cofactor of all transcription). Mediator is a very large multi protein complex that activates gene networks, critical for many gene promoters. Mediator has more than 30 subunits. It is vital for the action of Vitamin D. It is very large and allows many different protein interactions. It is highly correlated to the general function of RNA polymerase II in most transcription. Specific Mediator complexes occur in different kinds of cells and form chromatin loops that connect either two promoters or an enhancer and promoter.

All three molecules can combine to work together along with transcription factors to form the 3D chromatin shapes.


1) http://jonlieffmd.com/blog/vast-complexity-of-chromatin-3d-shapes
2) http://rstb.royalsocietypublishing.org/content/368/1620/20120369

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