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I'm taking a genetic engineering class at a local biohacker space. (Some of you might remember my attempts to teach myself a long time ago. Hopefully this will work better!) It just started, so we're still doing the preliminaries like learning how to pipette and extracting strawberry DNA, which is pretty great fun. During this week's class the subject of how DNA was prepared for Franklin's early crystallography attempts, and no one knew. So I volunteered to do some digging. The results are pretty interesting, despite the best efforts of Nature's paywalls to stop me, so I figured I'd share them here.
General notes:
DNA at this point was often referred to as "sodum thymonucleate", which is just DNA extracted from a calf thymus, sometimes written as NaDNA. Some references to other sources, but the thymus was definitely the predominate source. Lots of focus on how it changes with humidity, this was one of the causes of poor early x-ray results, as the samples had a mix of both forms.
First, the original publication in Nature announcing the double helix, which was immediately followed in the same issue with papers from Franklin and others filling in some of the details. They make a striking contrast in styles.
Crick and Watson paper with good annotations:
April 1953
Surprisingly informal, particular when compared with the papers that follow.
https://www.exploratorium.edu/origins/coldspring/printit.html
Molecular Structure of Deoxypentose Nucleic Acids
Wilkins, Stokes & Wilson
Immediately following in the same Nature, 1953
http://www.warrencountyschools.org/userfiles/2840/Classes/7795/wilkins.pdf
Molecular Configuration in Sodium Thymonucleate
Franklin and Gosling
Immediately following in the same Nature, 1953
https://www.ias.ac.in/article/fulltext/reso/009/03/0084-0088
Going back a bit earlier in the year, this from Franklin and Gosling is pretty great
The Structure of Sodium Thymonucleate Fibres. I. The Influence of Water Content
Franklin & Gosling March 1953
Some real details on how the "fibres" were prepared. Also found best x-ray pictures came from samples in a gel state, not dried. However, drying and then re-wetting can result in the best crystallized structure.
Lots of discussion of changes from the "A" to the "B" state due to humidty, multiple x-ray pictures that show how confusingly it could change based from experiment to experiment. Makes an interesting argument that because the phosphate groups can take up and release water so quickly, they must be on an exposed part of the chain instead of hidden in the center with the nucleotides on the outside as per Linus Pauling's model.
https://journals.iucr.org/q/issues/1953/08-09/00/a00979/a00979.pdf
Nucleic Acid: an Extensible Molecule?
By Wilikins in Nature, 1951
Speculates on a structure of nucleotide rings bonded together end on end
https://wellcomelibrary.org/item/b20048622#?c=0&m=0&s=0&cv=0
X-ray Studies of Nucleic Acids
By Astbury, 1947
X-ray pics weren't the best, but some real speculation on how the nucleotides could be joined together. Speculates on the nucleotides lying "immediately on top of one another like a great pile of plates, not disposed spiralwise round the long axis of the molecule" because of the density and approximate width of each nucleotide as they have worked out from x-rays. Experiments with physical models suggested a possible arrangement of nucleotides stacked this way, but they found some of the bonds unlikely. Mentions that x-rays of dried samples don't produce good pictures.
http://scarc.library.oregonstate.edu/coll/pauling/dna/papers/astbury-xray.html
But the best by far is this collection of Wilikins' papers and lab notes. Several forms of the following appear in the notes, typewritten at various dates in the 50s. Not clear what these were for, maybe instructing student new to the lab who got to do the grunt work? Very lengthy and detailed instructions with some annotations, one starting with the following:
It goes on to describe the extraction and filtering from there, using procedures not too different from what we did Tuesday.
https://wellcomelibrary.org/item/b20048658#?c=0&m=0&s=0&cv=45&z=-0.3843%2C0%2C1.7686%2C1.2266
General notes:
DNA at this point was often referred to as "sodum thymonucleate", which is just DNA extracted from a calf thymus, sometimes written as NaDNA. Some references to other sources, but the thymus was definitely the predominate source. Lots of focus on how it changes with humidity, this was one of the causes of poor early x-ray results, as the samples had a mix of both forms.
First, the original publication in Nature announcing the double helix, which was immediately followed in the same issue with papers from Franklin and others filling in some of the details. They make a striking contrast in styles.
Crick and Watson paper with good annotations:
April 1953
Surprisingly informal, particular when compared with the papers that follow.
https://www.exploratorium.edu/origins/coldspring/printit.html
Molecular Structure of Deoxypentose Nucleic Acids
Wilkins, Stokes & Wilson
Immediately following in the same Nature, 1953
http://www.warrencountyschools.org/userfiles/2840/Classes/7795/wilkins.pdf
Molecular Configuration in Sodium Thymonucleate
Franklin and Gosling
Immediately following in the same Nature, 1953
https://www.ias.ac.in/article/fulltext/reso/009/03/0084-0088
Going back a bit earlier in the year, this from Franklin and Gosling is pretty great
The Structure of Sodium Thymonucleate Fibres. I. The Influence of Water Content
Franklin & Gosling March 1953
Some real details on how the "fibres" were prepared. Also found best x-ray pictures came from samples in a gel state, not dried. However, drying and then re-wetting can result in the best crystallized structure.
Lots of discussion of changes from the "A" to the "B" state due to humidty, multiple x-ray pictures that show how confusingly it could change based from experiment to experiment. Makes an interesting argument that because the phosphate groups can take up and release water so quickly, they must be on an exposed part of the chain instead of hidden in the center with the nucleotides on the outside as per Linus Pauling's model.
https://journals.iucr.org/q/issues/1953/08-09/00/a00979/a00979.pdf
Nucleic Acid: an Extensible Molecule?
By Wilikins in Nature, 1951
Speculates on a structure of nucleotide rings bonded together end on end
https://wellcomelibrary.org/item/b20048622#?c=0&m=0&s=0&cv=0
X-ray Studies of Nucleic Acids
By Astbury, 1947
X-ray pics weren't the best, but some real speculation on how the nucleotides could be joined together. Speculates on the nucleotides lying "immediately on top of one another like a great pile of plates, not disposed spiralwise round the long axis of the molecule" because of the density and approximate width of each nucleotide as they have worked out from x-rays. Experiments with physical models suggested a possible arrangement of nucleotides stacked this way, but they found some of the bonds unlikely. Mentions that x-rays of dried samples don't produce good pictures.
http://scarc.library.oregonstate.edu/coll/pauling/dna/papers/astbury-xray.html
But the best by far is this collection of Wilikins' papers and lab notes. Several forms of the following appear in the notes, typewritten at various dates in the 50s. Not clear what these were for, maybe instructing student new to the lab who got to do the grunt work? Very lengthy and detailed instructions with some annotations, one starting with the following:
"Obtain approx. 5 lbs [for 20-25 grams DNA!] from freshly slaughtered calves at the New England Dressed Meat and Wool Co., Somerville. The glands must be ontains no more than 15 minutes after the animal has been killed. (It is good policy to tip foreman a $2.00 bill.) So there be no enzyeme action on DNA, which might degrade the product, the 5 lb.s of thymus must be imbedded in aprox. 40-50 lbs. of dry ica. A good procedure: Obtain a cardboard carton 2'2'2', and line bottom with 20 labs of dry ice. Immediately place thymus gland in carton and cover with remains amount of dry ice. Follow this procedure with every thymus gland and make sure the thymus is frozen stiff so that it will not become the LEAST BIT PLIABLE until use. If possible, place it into a refrigerator with dry ice. If it becomes at all pliable, discard and get new thymus."
It goes on to describe the extraction and filtering from there, using procedures not too different from what we did Tuesday.
https://wellcomelibrary.org/item/b20048658#?c=0&m=0&s=0&cv=45&z=-0.3843%2C0%2C1.7686%2C1.2266