Scientists edit single letters of DNA

  • Two teams of scientists unveiled a new generation of programmable molecular machines that can seamlessly repair tiny but deadly errors in the genetic coding of living organisms.
  • Taken together, the technologies expand the reach and precision of gene-editing, and open a path to fixing mutations that cause genetic blindness, sickle-cell anaemia, cystic fibrosis, and thousands of other debilitating diseases.
  • One approach, called base editing, performs “chemical surgery” directly on DNA, permanently altering faulty segments without cutting into the genome’s ladder-like structure.
  • The second technique corrects errors in another type of genetic material called RNA, where anomalies can also ruin health or lead to death.

First Method

  • The four chemical building blocks of DNA, called bases, are represented by the letters A, T, G and C, and always strung together in pairs — “A” with “T”, and “G” with “C”.
  • All it takes is one pair in the wrong place — a genetic mutation — for things to go horribly wrong.
  • Another gene-editing tool already in wide use called CRISPR-cas9 cuts the DNA strand, typically to insert or delete a DNA base pair.
  • But the new editing technique makes changes without breaking the DNA’s spiralling chain.
  • In a breakthrough last year, the research team showed how to swap a C-G for a T-A base pair.
  • Laboratories around the world successfully used the technique to fix so-called “point mutations” in organisms ranging from bacteria and corn to mice and human embryos.
  • But only about 15 percent of point mutations in humans known to be linked with disease can be fixed this way till now. 
  • The new tool — dubbed “ABE” for Adenine Base Editor — cleverly coaxes an A-T base pair into a G-C base pair, repairing a class of mutation that accounts for about half of the 32,000 known pathogenic point mutations in humans. 
  • Not only did the procedure have a much higher success rate than other gene-editing techniques, there were virtually no side-effects, such as unwanted DNA duplications or deletions.

Second Method

  • The human genetic code is about 3 billion letters long. 
  • That’s a lot of information, and these “letters”-the genetic bases adenine, cytosine, thymine, and guanine-are stored in nearly every one of the cells that makes up your body in the form of DNA.
  • Now, scientists have devised a way to fix a certain class of genetic errors by re-shaping the very molecules that form the basis of the genetic code. 
  • Researchers have modified CRISPR to edit the same types of errors out of RNA, which is closely related to DNA calling this new platform REPAIR.
  • The team genetically engineered an enzyme that literally rearranges the atoms of one kind of DNA base to turn it into another, all without disrupting the genetic material that surrounds it.
  • More than 50,000 human diseases, including sickle-cell anaemia and phenylketonuria, are the result of a single change in the genetic code-one letter out of three billion.
  • So it would be incredibly useful to have a technique whereby this so-called point mutation can be repaired without messing around too much with the surrounding DNA.

Source:Science Daily

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