OPINION
DOCTORS Lounge
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CRISPY Not Classic
Mary G. Barry, MD Louisville Medicine Editor editor @ glms. org
Were you born with sickle cell anemia? Maybe there is help at hand.
During the Civil War, the Austrian monk Gregor Mendel did experiments proving that plants inherited certain traits, and posited the existence of genes. In 1869, the Swiss physician Friedrich Miescher was first to notice and identify DNA as a separate entity by isolating what he called“ nuclein”( he studied pus). In 1879, Dr. Walther Flemming, a German military doctor, observed his own chromosomes and described their activity as“ mitosis.” Over the next two decades Theodor Boveri, a German biologist, worked with cell division( he studied worms), and said that chromosomes carry the genetic material, and that individual chromosomes carry different parts of it.
In 1928, the British biologist Frederick Griffith proved that Strep bacteria could be transformed from non-virulent strains into lethal ones while inside a mouse. In 1944, Oswald Avery, one of the first molecular biologists, along with Rockefeller Institute
colleagues McLeod and McCarty, showed that DNA was not a typical protein, but the actual hereditary molecule. The year I was born, Watson, Crick, Rosalind Franklin, and Maurice Wilkins discovered the double helix structure of DNA( Franklin was left out of the Nobel Prize, because she was female). In 1961, the US biochemist Marshall Nirenberg discovered how RNA works. In 1977, the British biochemist Frederick Sanger, with his partners, identified the amino acid sequences of DNA information, and DNA sequencing began in earnest. In 1983, US biochemist Kary Mullis’ refinements in DNA sequencing produced the polymerase chain reaction, which opened the door to rapid copying of DNA, to the tune of 100 billion in a few hours.
The Human Genome Project, thus enabled, began with planning in 1984 and launched in 1990. Millions of computer-hours and hundreds of scientists, with the help of $ 13 billion in worldwide and NIH funds, began mapping the entire human genome, finishing in April 2003. The genome map refers to complete sequencing of each chromosome, not a whole map of
any one person.
Meanwhile, after many years of work based on Francisco Mojica of Spain’ s discovery of short repeated DNA sequences, in 2002 Ruud Jansen et al. in Holland first coined the term CRISPR( Clustered Regularly Interspersed Palindromic Repeats). This refers to an adaptive immune mechanism whereby microbes defend themselves against invading viruses. The microbes record and then target the viral DNA so they can mount a precise counterattack. In 2005, Alexander Bolotin, a Russian immigrant working in France, found the large endonuclease enzyme CAS9 and the protein PAM, required for target acquisition and recognition. CAS stands for CRISPR Associated Protein. CAS9 is RNA-guided. It memorizes and then interrogates and precisely cleaves foreign DNA. After much work by many scientists, biochemists Jennifer Doudna and Emmanuelle Charpentier at Berkeley, and Gasiunas et al. in Lithuania showed that they could change the sequence of the inserter RNA to reprogram the CAS9 to target a site of their choosing.
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