Source:
Weizmann Institute of
Science, ScienceDaily
Rendering of bacteria. Bacteria have an immune system
to
fight off invasive viruses called phages, scientists say
|
But until
recently, scientists were not even sure that bacteria had a so-called adaptive
immune system -- one that "remembers" a past encounter to produce a
targeted response. That changed several years ago when a bacterial adaptive
system called CRISPR was discovered. The CRISPR immune mechanism is not just
crucial to the bacteria; it has a major impact on our daily lives: It is used
today, for example, to protect the "good" bacteria that make yogurt
and cheese. And it may also affect our future: Scientists have figured out how
to use the ingenious CRISPR system to "edit" the human genome --
making it a handy tool for a wide range of clinical applications.
To remember
an infection, the CRISPR system grabs a short sequence from the invading viral
DNA and inserts it straight into the bacterial genome. The bits of phage DNA
are stored in special sections of the genome; these form the immune memory. In
subsequent infections, CRISPR uses these sequences to create short strands of
RNA that fit the genetic sequence of the phages' kin. Protein complexes
attached to the RNA then identify the phage DNA and destroy it.
Selectivity
is clearly an issue for such a system: Previous research in Sorek's lab had
shown that mistakenly grabbing bits of self-DNA can cause the bacterial cell to
suffer a sort of autoimmune disease in which it attacks its own DNA, and the
results may be fatal to the bacteria. With around 100 times more self- than
foreign DNA inside the cell, says Sorek, there would seem to be room for many
more mistakes than researchers have actually observed.
How does the
CRISPR system know how to insert foreign, rather than self, bits of DNA into
the immune memory? Sorek and his research student Asaf Levy teamed up with
Prof. Udi Qimron and Moran Goren of Tel Aviv University to answer the question
in detail, revealing a complex, multi-step mechanism for this part of the
CRISPR process.
Looking more
closely at the results, the team found that the CRISPR system, using the
proteins Cas 1 and 2, specifically identifies DNA that replicates rapidly.
Thus, ironically, it is the phage's survival tactic -- its programmed drive to
replicate at all costs -- that proves to be its downfall.
"Still,"
says Sorek, "this did not completely explain how the CRISPR system
differentiates between self and non-self."
The solution
came from deeper understanding of the process. During DNA replication, small
breaks occur frequently in the DNA; these breaks call up a DNA repair enzyme
that "nibbles" a bit of the broken DNA. The team discovered that the
"leftovers" from the repair machinery's nibbling are actually the
source of the viral DNA used by the CRISPR system to generate the bacterium's
immune memory. But when that repair enzyme meets a short sequence called a
"Chi site," its nibbling stops. Such Chi sequences are found very
frequently throughout the bacterial genome, but rarely in the viral one. So Chi
sites also serve as "self" markers: They reject the activity of the
CRISPR machinery when they are present, but enable it to use bits of phage DNA
if they are missing.
Thus the
bacterial cell uses its normal DNA replication and repair processes to identify
phage DNA, checking and double-checking that the new DNA differs in two
fundamental ways from the "self" genome. Through the activity of the
two CRISPR proteins -- Cas1 and 2 -- the bacterial immune system can ensure it
is adding foreign DNA, alone, to its immune "memory," and can thus
activate its defenses.
Sorek:
"Solving the riddle of self-versus non-self for the bacterial immune
system and deciphering the exact mechanism of this step in the CRISPR process
gives us important insight into the unseen confrontation that is taking place
everywhere, all around us, all the time." Qimron: "The bacterial
solution to evading autoimmunity might be utilized in future clinical
applications that take advantage of the CRISPR system."
Journal Location
J. Peter
Etchells, Laxmi S. Mishra, Manoj Kumar, Liam Campbell, Simon R. Turner. Wood
Formation in Trees Is Increased by Manipulating PXY-Regulated Cell Division.
Current Biology, 2015; DOI: 10.1016/j.cub.2015.02.023
Weizmann
Institute of Science...
If you want to take the notice on the DNA then you have to take your blood sample and can see the magic that you can that it can not resemble with the other. You can also consult with the https://topamericanwriters.com/essayshark-com-review/ if you want to take all the related information.
ReplyDeleteThe DNA process has been quote easy now for the teachers to show to the children because they can now show them the complete process on their android vr head sets which are being now provided to them to clear their concepts in the classes. the children are quite happy as well that they are being given such amazing things that they can understand the concepts more clearly.
ReplyDeleteI am impressed by the details that you have shared in this post and It reveals how nicely you understand this subject. Complete rich content and fully informative. This information is meaningful and magnificent which you have shared here. I would like to thanks for sharing this article here. Tummy Tuck Recovery.
ReplyDeletePersonally I think overjoyed I discovered the blogs.
ReplyDeletecheck out here
It is good to hear that your store is now expanding to new locations. I have been a patron of Fantastic Eyes because of all the wonderful work that you guys do. I hope that this expansion move of yours will turn out to be successful. write my college paper I will definitely go and see this new store of yours
ReplyDeleteBacterial Cell Experimental and Research Methods in Metals Biotechnology. Bacterial cells in growth media are charged. wood floor water damage repair
ReplyDeleteBacteria are single-celled microorganisms. The cell structure is less complex than that of different creatures. nj construction
ReplyDelete