1993 Nobel Prize in Physiology or Medicine: Roberts and Sharp, Genes Were Found to Be Divided into Pieces

What You Will Learn in This Article

You will understand the surprising fact that genes are not continuous like source code, but are divided into several pieces. In 1977, Richard Roberts and Philip Sharp independently studied adenovirus genes and discovered that the sequences of DNA and mRNA do not exactly match, and that mRNA is assembled in a multi-part form. This discovery led to the concepts of exon and intron structures in eukaryotic genes, and mRNA splicing, which are now the basis of alternative splicing, gene therapy, mRNA vaccines, and splicing-modulating new drugs (SMA treatment Spinraza and Risdiplam).

A Story Different from Common Sense: Genes Contain Parts to Be Erased

Until the mid-1970s, the common understanding of genetics was clear: Gene = instruction for making a protein. The continuous sequence of DNA is transcribed into mRNA, and mRNA is translated into protein. This was the clear world established by Crick's central dogma.

This common sense was accurate for bacteria (prokaryotes), but not true for humans, animals, and plants (eukaryotes). Eukaryotic genes contain parts that are not reflected in the final protein (introns) interspersed between protein-coding parts (exons). When a gene is transcribed, the initially produced long pre-mRNA contains both exons and introns, and then, in a process called splicing, introns are removed, and only exons are joined together to create mature mRNA.

Here is an example of how different this discovery was from common sense: The human genome has about 3 billion base pairs, but only about 1.3% of it actually encodes proteins. A significant portion of the rest is introns and various regulatory sequences. While prokaryotic genomes are used densely, eukaryotic genomes have a sparse structure.

In the language of computer science, this is like source code with comments interspersed. The actual instructions are the exons, and the introns are comments or spacers that are removed during compilation. The compiler (spliceosome) recognizes specific sequences that mark the beginning and end of introns (GT-AG rule) and cuts out this part, joining only the exons.

Even more surprising is alternative splicing. A single gene can create multiple types of mRNA depending on the splicing method. By including some exons and excluding others, different protein isoforms are created. This is like creating multiple executables with conditional compilation (#ifdef) during compilation. It was later revealed that more than 90% of human genes undergo alternative splicing, which is the mechanism by which a much larger number of protein types are created from approximately 20,000 genes.

The impact of this discovery continues to expand. It has been revealed that splicing errors are the cause of several genetic diseases, and new drugs that target splicing have recently entered clinical trials.

The Zeitgeist: Post-Cold War World Reorganization and the Beginning of Korean Reforms

1993 was the year of the first post-Cold War world reorganization and the beginning of Korean political reform.

In world history, on September 13, the Israel-PLO Oslo Agreement was signed—Israeli Prime Minister Rabin and PLO Chairman Arafat shook hands on the White House lawn. A symbol of the Middle East peace. On November 1, the Maastricht Treaty took effect, officially launching the European Union (EU). On December, Russia's Yeltsin's new constitution was passed in a national referendum, establishing Russia's constitutional order after the collapse of the Soviet Union. The South African apartheid was in the process of being completely abolished, paving the way for Mandela's election the following year.

In technological history, on April 22, the Mosaic web browser was released, and Marc Andreessen's browser popularized the World Wide Web. This began the browser lineage that would lead to Netscape, Internet Explorer, Firefox, and Chrome. On July, Microsoft Windows NT 3.1 was released, integrating personal computing and server computing. Intel Pentium processor was released.

In Korean history, on February 25, President Kim Young-sam took office, marking the practical beginning of the civilian government. On August 12, the financial real-name system was implemented, a measure that was implemented overnight through a presidential emergency order, fundamentally changing the landscape of chaebols and political funds. On April, the Hana faction was disbanded, a decisive blow to military organizations, and a key factor in the reform of the army. On October 10, the Seohae ferry capsized, killing 292 people and exposing the flaws in South Korea's passenger ship safety system. This is the starting point of the sad lineage that would continue until the Sewol ferry disaster in 2014.

In this year of reorganization, the Nobel Committee recognized the two who had revealed the actual structure of genes. In a year when politics was re-editing old source code, the picture of how the source code of life is actually edited and used was recognized.

Richard Roberts: The Genetic Challenge of a Chemical Boy

Richard J. Roberts (1943~) is a British geneticist. His childhood story is an interesting example of Nobel Prize narratives.

The first pivotal moment was meeting a teacher in elementary school who sparked his academic interest. He learned the joy of mathematics and logic through the teacher's teachings.

The second was family support. His father, who was an automotive technician, provided him with various chemical experimental devices at home, allowing him to experiment happily. The experimental devices were very dangerous and even potentially explosive, but his parents encouraged his intellectual curiosity.

He received a Ph.D. in Chemistry from the University of Sheffield in 1968, and then switched to biology. He worked as a researcher at the Cold Spring Harbor Laboratory from 1972 to 1991, where he made the achievements that earned him the Nobel Prize. Since 1992, he has been the chief researcher at New England Biolabs, a leading company in restriction enzyme research and commercialization.

Philip Sharp: The Discovery of an MIT Cancer Researcher

Phillip A. Sharp (1944~) is an American geneticist. He received a Ph.D. from the University of Illinois in 1969, worked as a researcher at the Cold Spring Harbor Laboratory from 1971 to 1973, and has been a professor at MIT since 1979.

Sharp was studying gene expression of DNA viruses that cause cancer. The question he wanted to answer was clear: How is the genetic information of DNA transcribed into mRNA, and how is mRNA translated into protein? To visualize this, he designed an experiment to hybridize specific DNA fragments with the mRNA transcribed from that DNA and observe it with an electron microscope.

The Decisive Discovery: Loop Shapes Revealed by an Electron Microscope

The experimental discoveries of the two were dramatic.

Roberts' observation: While analyzing the base sequence of adenovirus, which causes colds, he discovered that the DNA sequence of a specific gene did not exactly match the sequence of mRNA transcribed from that DNA. There were parts that matched between DNA and mRNA, but they were not continuously connected and were scattered on the DNA.

Sharp's observation: In the DNA-mRNA hybridization experiment, he observed the results with an electron microscope. The original expectation was that the mRNA and DNA would perfectly match and attach side-by-side, but some parts of the observed mRNA were detached from the DNA and formed a loop. These loops corresponded to the introns—parts that are present in DNA but not in mRNA.

In 1977, the two presented their findings at a Cold Spring Harbor Laboratory symposium— it was completely independent research, but almost simultaneously. This discovery reorganized the fundamental picture of genetics.

Afterward, the detailed mechanism of splicing was elucidated. A large RNA-protein complex called the spliceosome recognizes the beginning and end of introns (GT-AG rule) and cuts them out, joining the exons. The rules, regulatory factors, and error mechanisms of splicing were elucidated in detail over the next 30 years.

CS Framework: Source Code with Comments and Conditional Compilation

Reconstructing the split gene system in the language of computer science results in the following diagram.

Gene = Source code with comments and executable code mixed together: Exons are executable instructions, and introns are comments that are removed during compilation. DNA is the original source, and mRNA is the compiled executable.

Spliceosome = Compiler Preprocessor: The spliceosome recognizes the beginning (5' splice site, GT) and end (3' splice site, AG) of introns and cuts them out, joining the exons. This is similar to how a preprocessor processes comments and macros.

Alternative Splicing = Conditional Compilation: Multiple executables are created from a single source code by including or excluding different parts depending on the condition. For example, in a single gene, a brain tissue-specific isoform and a muscle tissue-specific isoform are created through alternative splicing. This is similar to the #ifdef BRAIN ... #else ... #endif pattern.

Splicing errors = Compilation errors: If there is a mutation in the splicing site, introns are not properly removed, resulting in an incorrect protein. A significant portion of genetic diseases (β-thalassemia, DMD, etc.) are caused by this.

Exon shuffling = Reusable modules: During evolution, exons are reused between genes. The fact that a specific domain (immunoglobulin domain, etc.) is commonly reused in multiple genes is similar to the reuse of library functions in CS.

mRNA vaccines = Direct injection of assembly code: COVID-19 mRNA vaccines (Pfizer and Moderna) directly inject mRNA that encodes the spike protein. This bypasses the splicing process and goes directly to the translation stage. In essence, it injects the assembly code that creates the pathogen protein in human cells.

Splicing-modulating drugs = Manipulation of compilation options:

• Spinraza (nusinersen, 2016): Antisense oligonucleotide, induces the inclusion of exon 7 of the SMN2 gene, changing the treatment landscape for spinal muscular atrophy (SMA).
• Risdiplam (Evrysdi, 2020): Small molecule splicing modulator, oral drug for SMA treatment.
• Exon skipping therapy (Exondys 51, 2016): Induces skipping of a specific exon in Duchenne muscular dystrophy (DMD).

This analogy is not perfect. Splicing is probabilistic, regulated by tissue and developmental stages, and involves the cooperation of multiple factors. It is a much more sophisticated regulation than simple conditional compilation.

Academic Impact: A Fundamental Restructuring of Eukaryotic Genetics

Following this discovery, the field of eukaryotic genetics underwent a fundamental restructuring.

The Source of Protein Diversity: Thanks to alternative splicing, humans can produce over 200,000 different proteins from roughly 20,000 genes. More than 90% of human genes undergo alternative splicing, resulting in an average of 3-4 isoforms per gene.

Restructuring of Gene Annotation: After the completion of the Human Genome Project (2003), accurately mapping exons, introns, and splicing sites, rather than just the genome sequence, became a major focus in genetics. Today, databases like GENCODE and RefSeq provide this information.

Understanding Genetic Diseases: Splicing site mutations are found in approximately 15% of human genetic diseases. These include β-thalassemia, Duchenne muscular dystrophy (DMD), spinal muscular atrophy (SMA), and certain forms of cystic fibrosis (CF).

New Drugs Targeting Splicing:

• Spinraza (2016) — The first splicing-targeting therapeutic.
• Risdiplam (2020) — An oral splicing modulator.
• Exondys 51 (2016) — Induces exon 51 skipping in DMD.
• Casgevy (2023) — Uses CRISPR-Cas9 to treat sickle cell anemia and beta-thalassemia.

Growth of mRNA Technology: The understanding of splicing has advanced mRNA production and regulation technologies, which ultimately led to the COVID-19 mRNA vaccines (2020). The fact that the Pfizer, BioNTech, and Moderna vaccines saved humanity from the pandemic marks the culmination of this lineage.

Discovery of Long Non-coding RNA and MicroRNA: It was later discovered that the majority of the eukaryotic genome does not code for proteins, but this region expresses regulatory RNAs such as long non-coding RNA (lncRNA) and microRNA (miRNA). These discoveries are linked to the discovery of RNA interference by Fire and Mello (2006 Nobel Prize).

Korea's Legacy and Today

The impact of this lineage in Korea is also widespread. Since the late 1990s, research on splicing and RNA biology has been actively conducted in molecular biology laboratories at Seoul National University, Yonsei University, KAIST, and POSTECH.

Clinical Applications: At Seoul National University Hospital, Severance Hospital, Seoul Asan Hospital, Samsung Seoul Hospital, and Seoul St. Mary's Hospital, treatment with Spinraza, Risdiplam, and Zolgensma (gene therapy) for SMA patients has become standardized. Children who previously often died before the age of two can now develop normally.

Development of mRNA Vaccine Technology in Korea — Samsung Biologics, SK Bioscience, and Ijin are developing their own mRNA vaccine technologies. The infrastructure for developing mRNA-based new drugs has expanded in Korea since COVID-19.

RNA Sequencing Research: At Seoul National University, POSTECH, and KAIST, research using single-cell RNA sequencing (scRNA-seq) to map cell states and tissues is at a world-leading level. This research is creating cell- and tissue-specific maps of alternative splicing.

Why It Matters

What Roberts and Sharp left behind is the established concept that "the genes of eukaryotes are not simple continuous sequences, but rather are assembled from fragments."

This discovery revolutionized the fundamental understanding of eukaryotic genetics. The principles behind how humans can create over 100,000 proteins from 20,000 genes, how different protein isoforms are created at different stages of tissue and development, and how a significant portion of genetic diseases are caused by splicing errors all stem from this discovery.

A Symbol of Independent Discovery. Roberts and Sharp reached this discovery independently, in completely different laboratories. The confirmation of the same truth through different approaches is the power of scientific discovery.

The Beauty of a Personal Lineage — In Roberts' story, the support of his childhood mentor and parents leading up to the Nobel Prize symbolizes the power of education. The fact that his father provided a potentially explosive chemistry experiment kit at home eventually led to a person who changed the landscape of genetics in the late 20th century.

Following this award, the flow of research on RNA and gene regulation continued as follows:

• 2006, Fire and Mello — RNA interference (RNAi)
• 2009, Blackburn, Greider, and Szostak — Telomeres and telomerase
• 2020, Charpentier and Doudna (Chemistry) — CRISPR-Cas9 gene editing

The clinical and industrial applications of this discovery:

• Splicing-modulating therapeutics: Spinraza, Risdiplam, Exondys 51
• mRNA vaccines and therapeutics: COVID-19 Pfizer and Moderna vaccines
• Gene therapy: Zolgensma (SMA), Luxturna (Leber congenital amaurosis)
• Genetic diagnostics: Standardization of splicing site mutation testing
• Single-cell transcriptome analysis: scRNA-seq (cell mapping)

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