Question:
The amino acid side chains of the four histones in the nucleosome are subjected to remarkable variety of post-translation modifications such as phosphorylation, acetylation and methylation. Which one of the following post-translational marks on histone tails is usually associated with transcriptional repression?
- Acetylation of H3K9
- Methylation of H3K9
- Acetylation of H4K5
- Phosphorylation of H3S10
Rephrasing the question:
Which post-translational modification is associated with histones and transcriptional repression?
Answer:
Methylation of Histone 3 at the 9th lysine (H3K9) causes transcriptional repression (option 2).
Explanation:
Histones are the proteins that DNA is coiled around to (a) keep it compact, and (b) regulate its expression. Post-translational modifications can be made to histones to regulate how tightly DNA is wound around them, and thus to regulate how much transcription a gene in that area undergoes. (This falls under epigenetics.)
There are 5 families of histones: H1/H5, H2A, H2B, H3, and H4. H1/H5 are known as linker histones and the remaining four are known as core histones. This is because the core histones form the body of the nucleosome (two dimers of H2A + H2B, with a tetramer of H3 + H4) around which the DNA wraps. The linker histones bind the portion of DNA where it starts to wraps around the nucleosome and the portion where it stops wrapping around the nucleosome; in effect, it ‘locks’ the structure and position of the DNA around the nucleosome.
There are a number types of modifications a histone can undergo. These usually happen at the N-terminus ‘tail’ of the histone which sticks out from the main protein body, is rich in lysine (K) and arginine (R), and is highly positively charged.
The two most important modifications are methylation and acetylation. These are used to regulate gene expression. Other types of modifications, such as phosphorylation, SUMOylation, and ubiquitination, modify histone action, localization, and degradation.
There is a shorthand to describe such modifications. This is:
Histone number + amino acid on which modification occurs + type of modification + number of such modifications
So, for instance, H3K9Me1 means that on Histone 3 (H3), on its lysine-9 residue (K9), there is a single (1) methylation (Me).
Now, what do these modifications do? First let’s look at acetylation. This is the addition of a negatively-charged acetyl group to a lysine residue, which reduces the overall positive charge of the histone. Since DNA is negatively charged, making the histone less positive (= more negative) makes the DNA bind less tightly to the histone. This ‘more free’ DNA can then be transcribed more easily; so acetylation leads to transcriptional activation.
Next we have phosphorylation of serine, threonine, or tyrosine side-chains. Phosphate groups are also negatively charged, so histone phosphorylation also results in transcriptional activation. (It also has other roles, such as in DNA repair and chromatin condensation.)
Histone methylation is the addition of one or more methyl groups to lysine or arginine. Methylation of some amino acids causes gene activation, while methylation of other residues causes repression. This is because methylation does not have a straightforward effect on the charge of the histone. The effect it has depend on how other proteins recognize the methylated vs. non-methylated histones.
Luckily, in this question, there is only one option with methylation! So, option 2, the methylation of the lysine-9 residue of histone 3 will result in transcription repression.
Sources:
Histone at Wikipedia
Bannister AJ and Kouzarides T. (2011) Regulation of chromatin by histone modification. Cell Research 21, 381-395.
Does running a blog like this take a large attention-grabbing discussion is worth comment.
It’s difficult to find knowledgeable people using the same blog platform 바카라사이트”Anyways I am here now and would just like to say thank you for a marvelous post It’s on a completely different subject but it has pretty much the same layout and design.
hi Is there anybody 바카라사이트 having similar RSS problems? because i want to show my nudes and videos here but i can’t. If you want to see my pics kindly visit my webpage 😉 ,
i got 50$ per day 총판 in this website, you only do is visit or watching videos! dm me or visit my profile for more info!!! <3 😉 😉 ,
hello there
i have learn several just right stuff here. Definitely value bookmarking for revisiting.Aspectmontage makes it easy as can be and affordable for you to upgrade your windows, doors, roofing, showers or baths. “강남오피” this is kind of off topic but I need some guidance from an established blog. I will be coming back to your website for Perfect piece of work you have done, this internet site is really cool with wonderful info.
i have learn several just right stuff here. Definitely value bookmarking for revisiting Aspectmontage makes it easy as can be and affordable for you to upgrade your windows, doors, roofing, showers or baths“오피뷰”’m really impressed with your writing skills and also indow replacement Boston In addition to installing abode improvement products that compel your serene,
There most be a solution for this problem무료스포츠중계, some people think there will be now solutions, but i think there wil be one.
i have learn several just right stuff here. Definitely value bookmarking for revisiting.
I wonder how so much effort you place to make one of these fantastic informative web site.
온라인카지노” m really impressed with your writing skills and
We finalize our work space and hamper within your budget
, no matter what kind of programme you have in mind!
I like your blog it’s very good and informative , I do believe this is a great website. I stumbledupon it 😉 I’m going to return once again since I bookmarked it. Money and freedom is the greatest way to change 카지노사이트 Appreciate the helpful information Would you propose starting with a free platform like WordPress
I’ve been searching for hours on this topic and finally found your post. baccaratcommunity, I have read your post and I am very impressed. We prefer your opinion and will visit this site frequently to refer to your opinion. When would you like to visit my site?
Every game, Every gamer, All in one place. Welcome to Lucky Cola