Thomas A. Steitz

Thomas A. Steitz
Born	Thomas Arthur Steitz 8/23/1940
Birthplace	Milwaukee, Wisconsin, U.S.
Died	10/9/2018 Branford, Connecticut, U.S.
Nationality	American
Occupation	Biochemist, biophysicist, academic
Employer	Yale University, Howard Hughes Medical Institute
Known for	Structural studies of the ribosome, bio-crystallography
Education	Ph.D., Harvard University
Awards	Nobel Prize in Chemistry (2009), Gairdner International Award (2007)

Thomas Arthur Steitz (August 23, 1940 – October 9, 2018) was an American biochemist and biophysicist who spent the majority of his career investigating the three-dimensional structures of biological macromolecules. He held the position of Sterling Professor of Molecular Biophysics and Biochemistry at Yale University and served as an investigator at the Howard Hughes Medical Institute. Steitz is best known for his groundbreaking work in determining the atomic structure of the ribosome — the cellular machine responsible for translating genetic information into proteins — work that demonstrated that the ribosome is fundamentally a ribozyme, with its catalytic activity carried out by RNA rather than protein. For this achievement, he was awarded the 2009 Nobel Prize in Chemistry, shared with Venkatraman Ramakrishnan and Ada Yonath, "for studies of the structure and function of the ribosome." Over a career spanning more than five decades, Steitz made fundamental contributions to the understanding of DNA replication, transcription, and the mechanism by which antibiotics inhibit ribosomal function, work with profound implications for the development of new antibacterial drugs.

Early Life

Thomas Arthur Steitz was born on August 23, 1940, in Milwaukee, Wisconsin. His family lived in an apartment above a paint store in the downtown area of Milwaukee until 1949, when they relocated to Wauwatosa, a suburb west of the city. Growing up in Wauwatosa, Steitz attended local schools and developed an early interest in the sciences. He attended Wauwatosa High School, where he received his secondary education before going on to pursue studies in chemistry at the college level.

Steitz's upbringing in a middle-class Milwaukee household shaped his practical and industrious approach to scientific inquiry. His early years in Wisconsin provided the foundation for what would become one of the most distinguished careers in structural biology. The move to Wauwatosa placed the young Steitz in a community with strong public schools, and it was during his high school years that his aptitude for science became apparent.

Education

Steitz pursued his undergraduate education at Lawrence University in Appleton, Wisconsin, where he studied chemistry. Lawrence University, a small liberal arts college, provided Steitz with a rigorous scientific foundation. It was during his time as an undergraduate that he first encountered the emerging field of structural biology, which would define his career.

After completing his bachelor's degree at Lawrence, Steitz enrolled in the doctoral program in molecular biology and biochemistry at Harvard University. He pursued his Ph.D. under the supervision of William N. Lipscomb Jr., a Nobel laureate in chemistry. Steitz's doctoral thesis, titled "The 6Å crystal structure of carboxypeptidase A," was completed in 1967 and represented one of the early applications of X-ray crystallography to the study of enzyme structure. This work placed Steitz squarely within the tradition of structural biology that was transforming the understanding of biological molecules at the atomic level.

Following the completion of his doctorate, Steitz undertook postdoctoral research at the Medical Research Council (MRC) Laboratory of Molecular Biology in Cambridge, England, where he worked under David M. Blow. It was during this period that Steitz heard Max Perutz speak about the structure of myoglobin, the first protein to be solved at the resolution of individual atoms — an experience that left a lasting impression and further cemented his commitment to X-ray crystallography as a tool for understanding biological function. The MRC Laboratory was at the time the world's foremost center for structural biology, and Steitz's postdoctoral work there provided him with training in the cutting-edge techniques he would employ throughout his career.

Career

Early Academic Career

After completing his postdoctoral training in Cambridge, Steitz held a position at the University of California, Berkeley, before joining the faculty at Yale University, where he would remain for the rest of his career. At Yale, Steitz rose through the academic ranks to become Sterling Professor of Molecular Biophysics and Biochemistry, one of the university's most distinguished faculty titles. He was also appointed as an investigator at the Howard Hughes Medical Institute, which provided sustained funding and support for his research over many years.

Throughout the 1970s and 1980s, Steitz applied X-ray crystallography to a succession of increasingly complex biological macromolecules. His laboratory became one of the leading structural biology groups in the world, tackling problems related to DNA polymerases, RNA polymerases, and other components of the molecular machinery of gene expression. His approach was characterized by an insistence on obtaining high-resolution crystal structures and combining structural data with biochemical experiments to elucidate function.

Structural Studies of DNA and RNA Polymerases

Before his Nobel Prize–winning work on the ribosome, Steitz made significant contributions to the understanding of enzymes involved in DNA replication and RNA transcription. His structural studies of DNA polymerases — the enzymes responsible for copying DNA — provided atomic-level detail about how these molecules recognize and process genetic information. These studies helped explain the fidelity of DNA replication and the mechanisms by which polymerases proofread newly synthesized DNA strands.

Steitz's work on RNA polymerases and other components of the transcription apparatus similarly advanced the understanding of how genetic information encoded in DNA is transcribed into messenger RNA. His structural studies illuminated the catalytic mechanisms of these enzymes and their interactions with nucleic acid substrates, establishing principles that are now fundamental to molecular biology.

The Ribosome: Structure and Function

The work for which Steitz is most celebrated is his determination of the atomic structure of the large (50S) subunit of the ribosome. The ribosome is the molecular machine present in all living cells that translates the genetic code carried by messenger RNA into proteins. It consists of two subunits — a large subunit and a small subunit — each composed of ribosomal RNA and dozens of proteins. Understanding the three-dimensional structure of the ribosome at atomic resolution had been one of the grand challenges of structural biology for decades.

In August 2000, Steitz and his colleagues at Yale published the crystal structure of the large ribosomal subunit from the archaeon Haloarcula marismortui at 2.4 angstrom resolution. This landmark achievement, described by Yale as analogous to "climbing Mount Everest," revealed the detailed atomic architecture of the ribosome's catalytic core. The structure was obtained using X-ray crystallography at synchrotron radiation facilities, and its solution required overcoming enormous technical challenges related to the size and complexity of the ribosomal subunit, which contains approximately 100,000 atoms.

The most important insight to emerge from Steitz's ribosome structure was the demonstration that the peptidyl transferase center — the site within the ribosome where peptide bonds are formed during protein synthesis — is composed entirely of RNA, with no protein within approximately 18 angstroms of the active site. This finding provided direct structural evidence that the ribosome is a ribozyme — an RNA molecule that functions as an enzyme — and strongly supported the "RNA world" hypothesis, which posits that RNA preceded proteins as the catalytic workhorse of early life.

Steitz showed that the peptidyl transferase reaction — the formation of the peptide bond that links amino acids together in a growing protein chain — was catalyzed by RNA and not by protein components of the ribosome. This represented a paradigm shift in the understanding of how protein synthesis occurs and had profound implications for evolutionary biology, as it suggested that the ribosome, and thus protein synthesis itself, originated in an RNA-dominated world before the evolution of protein enzymes.

Antibiotics and the Ribosome

Beyond determining the fundamental structure of the ribosome, Steitz made important contributions to understanding how antibiotics interact with the ribosome to inhibit protein synthesis. Many of the most commonly used antibiotics — including macrolides, chloramphenicol, and lincosamides — work by binding to the ribosome and blocking its function. By determining crystal structures of the large ribosomal subunit in complex with various antibiotic molecules, Steitz and his team revealed, at atomic resolution, the precise binding sites and mechanisms of action of these drugs.

This work had significant implications for medicine and drug development. By showing exactly how antibiotics bind to the ribosome and interfere with protein synthesis, Steitz's structures provided a rational basis for designing new antibiotic drugs, an endeavor of increasing urgency given the rise of antibiotic-resistant bacteria. His structural data enabled pharmaceutical researchers to understand why certain mutations in bacterial ribosomes confer resistance to specific antibiotics and to envision strategies for developing next-generation antibiotics that could overcome such resistance.

Steitz published a landmark study detailing the atomic arrangement of the large ribosomal subunit, and subsequent work from his laboratory mapped the binding sites of numerous clinically important antibiotics to this structure. These findings established Steitz as a central figure not only in fundamental structural biology but also in the applied field of antibiotic drug design.

Mentorship and Laboratory

Throughout his career at Yale, Steitz mentored numerous graduate students and postdoctoral researchers who went on to become leaders in structural biology and related fields. Among his notable students was Nenad Ban, who later became a professor at ETH Zurich and made his own significant contributions to ribosome structural biology. Steitz was described by colleagues as a "remarkable person, scientist and mentor" who combined exacting scientific standards with personal generosity and support for his trainees.

The Steitz laboratory at Yale was known for its systematic and rigorous approach to crystallographic studies. Steitz had an "unerring" instinct for identifying the most important structural problems in molecular biology and for devising experimental strategies to solve them. His laboratory produced a series of high-impact structures throughout the 1990s and 2000s that transformed the understanding of nucleic acid–protein interactions and the molecular machinery of gene expression.

Personal Life

Thomas Steitz was married to Joan A. Steitz, a molecular biologist who is also a Sterling Professor at Yale University and an investigator at the Howard Hughes Medical Institute. Joan Steitz is known for her pioneering work on RNA biology, including the discovery and characterization of small nuclear ribonucleoproteins (snRNPs). The couple represented one of the most distinguished partnerships in modern molecular biology.

Thomas Steitz died on October 9, 2018, in Branford, Connecticut, at the age of 78. His death was mourned across the scientific community, with tributes published in Nature, Science, and numerous other journals and institutions. Colleagues remembered him for both his scientific achievements and his personal qualities, including his dedication to training the next generation of structural biologists.

Recognition

Thomas Steitz received numerous awards and honors over the course of his career, reflecting the significance of his contributions to structural biology and biochemistry.

His most prominent distinction was the 2009 Nobel Prize in Chemistry, which he shared with Venkatraman Ramakrishnan and Ada Yonath "for studies of the structure and function of the ribosome." The Nobel Committee recognized the trio's independent but complementary work in determining the atomic structures of the ribosomal subunits, work that fundamentally transformed the understanding of one of the most essential molecular machines in biology.

In 2007, Steitz was awarded the Gairdner International Award, one of the most prestigious prizes in biomedical science, "for his studies on the structure and function of the ribosome which showed that the peptidyl transferase was an RNA catalyzed reaction, and for revealing the mechanism of inhibition of this function by antibiotics." This award recognized both the fundamental biological insights of his ribosome work and its medical relevance.

Steitz was elected as a Foreign Member of the Royal Society (ForMemRS), one of the highest honors for scientists internationally.

In 2010, Lawrence University, his undergraduate alma mater, honored Steitz for his Nobel Prize achievement, recognizing him as one of the institution's most distinguished alumni.

Legacy

Thomas Steitz's contributions to science are central to the modern understanding of how biological macromolecules function at the atomic level. His structural studies of the ribosome provided the definitive evidence that protein synthesis is catalyzed by RNA, a finding that reshaped thinking about the origins of life and the evolutionary relationship between nucleic acids and proteins. The demonstration that the ribosome is a ribozyme remains one of the most important discoveries in molecular biology of the late twentieth and early twenty-first centuries.

His work on the ribosome also had direct practical consequences. The atomic-resolution structures of ribosomal subunits in complex with antibiotics provided a structural framework for rational antibiotic drug design, an area of research that continues to build on Steitz's foundational work as the challenge of antibiotic resistance grows globally.

The National Institutes of Health noted that Steitz's ribosome structure was among the "countless groundbreaking discoveries in biology and medicine" associated with Yale University over the past two centuries, placing his achievement in the context of a long tradition of scientific excellence.

Beyond his specific research contributions, Steitz's career exemplified the power of X-ray crystallography as a tool for biological discovery. Beginning with his doctoral work on carboxypeptidase A in the 1960s and continuing through his Nobel Prize–winning studies of the ribosome in the 2000s, Steitz consistently pushed the boundaries of what crystallographic methods could reveal about biological function. His laboratory trained a generation of structural biologists who have carried forward his approach and expanded it to new biological systems.

The scientific community's response to Steitz's death in 2018 — with extensive obituaries in Nature, Science, Chemistry World, and other leading publications — reflected the breadth and depth of his impact on the field. His work continues to inform research in molecular biology, evolutionary biology, and pharmaceutical development.