Letters to Peter

Linus and Peter Pauling at Warwick Castle, England. 1948.

Linus and Peter Pauling at Warwick Castle, England. 1948.

“You know how children are threatened ‘You had better be good or the bad ogre will come get you.’ Well, for more than a year, Francis and others have been saying to the nucleic acid people at King’s ‘You had better work hard or Pauling will get interested in nucleic acids.’”

Peter Pauling. Letter to Linus Pauling, January 13, 1953.

Normally, when Linus Pauling became interested in something, he would dive headlong into it. Hours and hours of his time, over weekdays and weekends, would be committed to research in pursuit of fleshing out every last useful detail. This arduous process is best illustrated by his work on the nature of the chemical bond, work which would later win him a Nobel Prize in Chemistry.

Pauling’s experience with DNA, however, was not an example of this typical approach.

First, it should be noted that Pauling did not have years to spend working on DNA. Its importance was fully realized in the summer of 1952, less than a year before Watson and Crick elucidated its structure, and although Pauling actually began studying nucleic acids as early as 1933, he wasn’t able, or willing, to spend a significant amount of time on a molecule that was perceived to be relatively unimportant.

Even after learning of the importance of DNA, Pauling still didn’t make time for it. As emphasized in earlier posts on Linus Pauling and DNA, Pauling remained very much preoccupied with his work on the nature of proteins.

An examination of Pauling’s correspondence with his son Peter – a man uniquely positioned in the middle of the DNA story – reveals that other matters, many of them trivial, also took precedence over Pauling’s pursuit of the structure of DNA.

In the fall of 1952, Peter Pauling, an aspiring crystallographer and the second oldest of the four Pauling children, began his graduate studies at the University of Cambridge. Coincidentally, James Watson and Francis Crick were also at Cambridge at this time, and not long after his arrival, Peter had met them, become an office-mate, and was spending off-hours time with the duo.

Because Linus Pauling and the Watson-Crick tandem were both attempting to solve the structure of DNA, Peter’s arrival at Cambridge gave his father an excellent opportunity to keep tabs on the work being done by his competitors in England. A close examination of the voluminous father-son correspondence from this era suggests, however, that DNA was far from a pressing topic in Pasadena.

Also, as to your curtains: will you check the dimensions and let us know. You say in your letter two windows 6’ 6” high, 50” and 37” wide respectively, in other words four curtains each 48” wide. Mama thinks that you probably mean four curtains each 36” wide. It would be hard to get the wider material.

Also, would you write us as to the exact points between which the vertical dimensions are measured. What is the distance from, say, the top of the window frame (or some other exactly specified locus) to the floor, and also to the bottom of the window frame? Mama thinks that probably the curtains should reach all the way to the floor, but in any case they should extend from the top of the window frame to the bottom of the window frame (if you have window frames), or from a point a little below the opening at the bottom. She suggests that one of your old curtains might serve for one of the windows, and that she would then have to make only a pair for the larger window.

I sympathize with you about the bed. I remember sleeping on a bed which had a two by four across under my ear; it was not very comfortable.

-Linus Pauling, letter to Peter Pauling, October 22, 1952.

Linus first wrote to Peter in England on October 22, 1952. By this time, the elder Pauling was well aware of the importance of DNA, but had not yet devised a structure. Watson and Crick, on the other hand, had developed a structure for DNA a year earlier. Although their model turned out to be incorrect, the two men continued their work with nucleic acids. Clearly, for Watson and Crick, DNA was becoming extremely important. For Pauling this did not appear to be the case – although Watson and Crick were both mentioned in this first letter, DNA was not.

As it turns out, other subjects – including, but not limited to, curtains for Peter’s new apartment, recent travels and upcoming travel plans, finances, and, of course, cars – were much more prevalent than was DNA in the Paulings’ early correspondence.

As time went on, nucleic acids naturally became a slightly larger topic, though never did they assume center stage. Take, for example, this letter sent from Linus to Peter on February 4, 1953. By the time of its authoring, Linus Pauling had completely developed his structure, and had also sent off his manuscript for publication, a development which merited one paragraph worth of description. The rest of the letter is used to discuss, in great detail, Pauling’s plans to travel to England and also his keen interest in purchasing a new Riley from the U.K.-based International Motors. (Being something of a family obsession, cars were a very popular subject in many of the letters between Linus and Peter.)

In another letter from Pauling to Peter written on March 10, 1953, DNA plays a much larger role. This time, about half of the three-page document is dedicated to discussing various aspects DNA; the remainder focuses on travel plans and automobiles.

Peter Pauling, December 1954.

Peter Pauling, December 1954.

The other letters follow this same trend. Clearly, Linus and Peter’s lengthy discussions on subjects such as cars, traveling, curtains, and other aspects of science suggest that Pauling wasn’t interested in DNA on the level of certain other scientific pursuits.

Another interesting aspect of the correspondence between Linus and Peter Pauling is the opportunity that it provides for tracking the evolution of the consensus response to Pauling’s structure.

As might be expected, Peter’s reaction stayed upbeat throughout all of their letters. However, as time progressed, it is clear that Peter became less-confident that his father had solved DNA. For example, in a few of the earlier letters, Peter mentions that Watson and Crick earlier devised and discarded a structure similar to the Pauling-Corey triple helix, but that the opinion at the Cavendish Laboratory is that Pauling’s structure is a good one, albeit “pretty tight.”

From that point on though, Peter begins talking less about Pauling’s structure, and more about work being done by Watson, Crick, and Rosalind Franklin. One might deduce that, although Peter didn’t specifically issue a disagreement with his father’s structure, he did develop a certain degree of skepticism as time progressed. Peter also does not often mention other opinions of his father’s structure, most likely because, upon further examination, it was not well-received by the English contingent.

Peter Pauling Discusses His Father’s Strengths and Personality

For more information on DNA, please visit the Race for DNA website. For more information on Linus Pauling, check out the Linus Pauling Online portal.

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The Pauling-Corey Structure of DNA

Today, the structure of DNA series is continued with the model proposed by Linus Pauling and Robert Corey in 1953. As a result of insufficient data and an overloaded research schedule, Pauling’s structure turned out to be incorrect. However, it is interesting to see the ways in which one of the world’s leading scientists went wrong with his approach to the structure of this hugely-important molecule.

Linus Pauling played around with nucleic acids as early as 1933 when he hypothesized a structure for guanine, a base ring. In the summer of 1951, he again became interested in DNA when he heard that Maurice Wilkins at King’s College had developed a few good photographs of nucleic acids. Unfortunately for Pauling, Wilkins was unwilling to share his research. In November of that same year, a structure of nucleic acids was proposed and then published by Edward Ronwin. Pauling could tell almost immediately that Ronwin’s structure wasn’t correct, but it did contain a few good ideas that got him thinking about other possible structures. Pauling hypothesized that DNA was likely helical in shape, with the large base groups facing out and the phosphate groups stacked in the core. At this juncture, however, Pauling was again distracted by other research and let the project drop.

Until 1953 nucleic acids weren’t considered to be very important. At the time, proteins, rather than DNA, were considered by most scientists to be the carriers of genetic material. Partly because of this, Pauling’s attention was focused on proteins, not DNA. In May of 1952, Pauling was scheduled to attend a special meeting of the Royal Society where he would address questions pertaining to his protein structures. This trip would also give him an opportunity to discuss DNA with Rosalind Franklin, who was Maurice Wilkins’ assistant. She had recently developed an especially clear photograph of DNA which likely would have saved Pauling from making some key mistakes when determining the structure of DNA.

As a result of his very-public anti-war and anti-nuclear activities, Pauling’s initial request for a passport was denied, though he was granted a limited passport only ten weeks later. However, when Pauling arrived in England, he did not visit King’s College. He was preoccupied with his protein research and he assumed that Wilkins still wouldn’t be willing to share his data.

Soon after his visit to England, Pauling was granted a full passport and traveled to France. Here he was informed, through an experiment performed by Alfred Hershey and Martha Chase, that DNA was in fact the genetic master molecule. Upon learning this, Pauling decided that he would solve the structure of DNA. However, when he returned to California, he continued to work primarily with proteins. It wasn’t until November 25, 1952 that Linus Pauling would make a serious attempt at the structure of DNA.

Unfortunately, when Pauling did decide to put in some time with DNA, he still had insufficient data to correctly deduce its structure. Using only a few blurry x-ray patterns done by William Astbury in the 1930s and a photograph published by Astbury in 1947, Pauling decided that DNA was indeed a three-chain helix with the bases facing outward and the phosphates in the core.

Astbury's 1947 photographs of DNA.

Astbury's 1947 photographs of DNA.

However, it was immediately clear that making room for so many phosphates in the center of the molecule would be quite a task. Pauling spent a great deal of time manipulating his model, and eventually produced a satisfactory representation. He then asked Robert Corey, his chief assistant at Caltech, to perform detailed calculations on the proposed atomic positions. Corey’s calculations proved that, despite Pauling’s efforts, there still wasn’t enough room for all of the atoms. Pauling, refusing to consider the possibility that his structure was incorrect, resorted to further manipulation. (In fact, Pauling refused to concede even after a colleague pointed out that there was no room for sodium ions in the core of his model, a feature that is essential in the creation of sodium salts of DNA.) Convinced that the finer details would later fall into place, Pauling and Corey spent the last week of the year writing up their structure, and on the last day of 1952, they submitted “A Proposed Structure for the Nucleic Acids” to the Proceedings of the National Academy of Sciences.

Diagram of the Pauling-Corey structure for DNA, as published in PNAS.

Diagram of the Pauling-Corey structure for DNA, as published in PNAS.

The paper was uncharacteristic of Pauling. Instead of his usual confidence, he stated that the structure was “promising” but also “extraordinarily tight.” Pauling likewise noted that the model accounted only “moderately well” for the x-ray data, and that the atomic positions were “probably capable of further refinement.” As it turned out, Pauling wasn’t seeking perfection with his structure. In reality, he wanted to be the first to publish a roughly correct structure of DNA. Rather than having the final say, he wanted the first.

Once the article was published in February of 1953, it became more and more apparent that Pauling’s structure wasn’t even roughly correct. By this time, Pauling had already moved on to other projects, and was surprised at the fact that his paper was received so poorly. Once he caught wind of the talk surrounding his structure, he decided to return to the topic of DNA. Despite the negative reaction, Pauling still believed that his structure was essentially right. However, he soon received better nucleotide samples from Alex Todd, an organic chemist at Cambridge, and began a more rigorous approach to determining the structure of DNA.

Unfortunately, by this time it was too late. Upon the publication of Pauling’s unsatisfactory model, James Watson and Francis Crick were given the green light to pursue their own model of DNA. Before long, Pauling saw that the work they were doing was very promising. A few days after first seeing their structure, Pauling received an advance copy of the Watson and Crick manuscript. At this point, he still retained a fair amount of confidence in his own model, but acknowledged that there was now another possible model. In a letter to Watson and Crick written on March 27, 1953, Pauling noted

I think that it is fine that there are now two proposed structures for nucleic acid, and I am looking forward to finding out what the decision will be as to which is incorrect.

However, he had still not seen Rosalind Franklin’s data; Watson and Crick had. (Interestingly enough, Robert Corey had traveled to England in 1952 and viewed Franklin’s photographs. It is unknown whether or not he purposely failed to provide Pauling with the details of the images.)

This fact would soon change. In April of 1953, Pauling was to attend a conference on proteins in Belgium. On his way, he stopped in England to see the Watson and Crick model of DNA as well as Franklin’s photographs. After examining both, Pauling was finally convinced that his structure was wrong and that Watson and Crick had solved DNA.

Linus Pauling, although disappointed with the results, accepted his defeat graciously. He gave Watson and Crick full credit for their discovery and assisted them in tying up a few loose ends with their model. For Pauling, this event was a single failure in a sea of successes. In fact, the very next year, he would win the Nobel Prize in Chemistry – the first of his two Nobel Prizes. Despite his embarrassing mistakes, Pauling was to remain in good standing with the scientific community.

Please check back on Thursday for the conclusion of the DNA structure series – an examination of the correct structure deduced by Watson and Crick. For more information on DNA, please visit the website Linus Pauling and the Race for DNA. For more information on Linus Pauling, visit the Linus Pauling Online Portal.