Deoxyribonucleic acid, more commonly known as DNA, is a self-replicating chain of nucleotides which is present in all living organisms and carries genetic information required for the growth, development and functioning of all organisms. Since the discovery of the DNA double helix molecule by molecular biologists Francis Crick and James Watson in 1953, an incredible amount of time and money has been invested in researching this basic building block of organic life.
The ability to synthesize DNA through chemical processes is undoubtedly a marvel among modern technological advances and figures into a wide array of industry sectors. DNA synthesis and other synthetic biology techniques are being used by chemical companies like DuPont to make rubber, paint acrylics and surfactants for blending oil and water. Other companies are using synthesized DNA to aid in the development of pharmaceutical treatments such as cancer immunotherapies. The synthesis of DNA molecules which are typically found only in living organisms such as spiders is even helping in the development of super-strong, super-soft fibers that exhibit many of the characteristics of silk. A recent market research report from Allied Market Research indicated that the global synthetic biology market is expected to rise by a compound annual growth rate (CAGR) of 44.2 percent from 2014 to 2020 to reach a total value of $38.7 billion by 2020. DNA synthesis is both the largest segment of this market and the segment which is expected to grow quickest at a CAGR of 57.8 percent.
This Tuesday, July 3rd, marks the 34th anniversary of the issue of one of the seminal patents in the field of DNA synthesis. The lead inventor, Marvin Caruthers, is a member of the 2018 class of inductees into the National Inventors Hall of Fame. As we approach this milestone, we once again revisit our Evolution of Technology series to take a good look at the history of DNA exploration and gain a better understanding of the important innovations conceived of by Caruthers which continue to play a major role in forensics, pharmaceuticals, chemical manufacturing and other industries.
The History of DNA, From the Origin of Species to the Double Helix
Humanity’s understanding of the importance of genetics began to come to fruition in the 19th century thanks to such scientists as Charles Darwin and Gregor Mendel. The Origin of Species, published by Darwin in 1859, is the foundational text for the science of evolution and is often hailed as the basis of the argument for hereditary evolution in which subsequent generations of a species gain new traits which enable those later generations of the species to better adapt to their living environment. Mendel, an Augustinian monk, is considered to be the father of genetics thanks to his experiments with multiple generations of pea plants. Not only did Mendel establish that certain traits of pea plants, like height, color and seed shape, are hereditary, he also established the concept of dominant and recessive genes in relation to those inherited traits.
It would take well into the 20th century before scientists were able to make the discovery as to what allowed living organisms to pass on desirable traits to the next generation through their offspring. This is despite the fact that Swiss physician Friedrich Miescher had isolated DNA from human organic material back in 1869. In 1902, the British physician Sir Archibald Edward Garrod was the first to apply Mendel’s theory on inherited traits, originally only discovered in plant life, to human biological processes, especially disease traits which are inherited from one generation to the next. Beginning in the 1920s, American scientist Barbara McClintock would take Mendel’s genetic theories many steps further while working with chromosomes of the crop plant maize to determine the mechanisms by which chromosomes exchange information as well as various chromosomal regions and their differing roles in biology.
Through the middle parts of the 20th century, both the importance and the structure of DNA would come into much greater focus. Although DNA had been discovered and isolated and scientists had some knowledge of inherited traits and diseases, it took the work of Canadian-American physicist Oswald Avery to make the connection that DNA was the carrier of genes within cells; his findings were published in 1944. The basis of DNA as genetic material was further confirmed in 1952 with a series of experiments known as the Hershey-Chase experiments which found that bacteriophages infect other bacterial cells by transmitting DNA into the host cell, not proteins which many other scientists had theorized. Although the helix shape for DNA had been theorized, it was Crick and Watson who discovered the double helix structure for DNA which enabled the replication of DNA for passing on genetic traits.
Marvin Caruthers and the Synthetic Production of DNA Molecules
The discovery of DNA and its importance on biological processes for all life, not just human life, was a major advance for the science of biology. The idea that DNA could be synthesized outside of the body of living organisms, however, was a bridge too far until the work of Marvin Caruthers provided the breakthrough necessary for this next step in biology.
Born in February 1940 in Des Moines, Iowa, Caruthers earned a bachelor’s degree in chemistry from Iowa State University in 1962 and would go on to earn his Ph.D. in biochemistry from Northwestern University in 1968. At Northwestern, Caruthers met and worked under the tutelage of Robert Letsinger, the first of a trio of scientists who Caruthers would later credit with shaping his own scientific career. Through the 1960s and 1970s, Caruthers was exposed to many early experiments in the field of synthesizing DNA molecules on insoluble polymers and other platforms. His work focused on improving the reliability of DNA synthesis, work that he would continue after moving on from Northwestern to both the University of Wisconsin-Madison and the Massachusetts Institute of Technology. Caruthers would become a professor of biochemistry at the University of Colorado at Boulder in 1980, where he continues to serve as a Distinguished Professor.
The first of two patents for which Caruthers is inducted into the National Inventors Hall of Fame is U.S. Patent No. 4415732, titled Phosphoramidite Compounds and Processes. Issued November 15th, 1983, it covers a new class of nucleoside phosphoramidites, that are derivatives of saturated secondary amines, which are relatively stable to permit isolation thereof and storage at room temperature. Phosphoramidites, or monomides of a phosphite diester, have a high reactivity towards nucleophiles that are catalyzed by weak acids and are useful in the synthesis of DNA and other nucleic acids. The invention provides phosphoramidites that serve as intermediates for polynucleotide synthesis and an improved process for producing oligonucleotides, DNA molecules with applications for genetic testing and forensics, by enabling a more efficient process of forming internucleotide bonds.
July 3rd is the anniversary date for the issue of the second patent for which Caruthers has been inducted: U.S. Patent No. 4458066, titled Process for Preparing Polynucleotides. Issued in 1984, it claims a modified inorganic polymer for preparing new and useful intermediate nucleotides as well as processes for conversion to oligonucleotides that are especially useful for the synthesis of both DNA and ribonucleic acid (RNA). The use of the modified inorganic polymer as a support structure in this invention is useful in the addition of nucleosides or oligonucleotides to an original nucleoside moiety while reducing the number of steps needed for the separation and purification of products at each stage to ensure proper sequencing of the added nucleosides.
Caruthers’ lasting legacy will be his work to develop more stable solid substrates to which growing DNA molecules could be attached as well as methods for manufacturing and shipping DNA synthesis reagents on a commercial scale. He would go on to co-found successful biotech companies including Amgen and Applied Biosystems. The holder of 43 U.S. patents, he has received numerous professional recognitions throughout his career, such as being named a Guggenheim Fellow in 1981; being named a member of both the American Academy of Arts & Sciences and the National Academy of Sciences in 1994; earning the National Medal of Science in 2006; and receiving both the National Academy of Sciences Award in Chemical Sciences and the ACS Award for Creative Invention in 2014.