New York State of Mind

Born in Brooklyn, NY on Christmas Eve, 1947, Lambowitz’s fascination with science did not stem primarily from school or family, though both areas gave him a good deal of exposure. “I attended Stuyvesant High School, ” he says of the Manhattan institute, “which is a specialized science school with a longstanding tradition, much like Bronx Science. One of my uncles was a chemist and another was in the book business, and, between the two, they provided many science books that I would otherwise not have had an opportunity to read.” More than anything else fostering his interest in science, recalls Lambowitz, was his time spent at the American Museum of Natural History in New York. “I was fascinated by that museum and spent a lot of time there while I was growing up, ” he says, “and became interested in biology and natural history as a direct result. Even Brooklyn had world-class libraries and museums, which I took for granted at the time. For a kid whose parents didn’t graduate college, this type of thing can have a huge impact.”

After finishing high school, Lambowitz stayed close to home and attended Brooklyn College (New York), pursuing a degree in chemistry “so I could ultimately come back to biology from a more detailed and molecular perspective, ” he says. After receiving his bachelor of science degree in 1968, Lambowitz began graduate studies at Yale University (New Haven, CT). He initially joined a laboratory studying the phenomenon of senescence using the fungus Podospora as a model. “It could only grow for a finite amount of time, and that amount of time was genetically determined, and the determinants were found in mitochondria, suggesting mitochondrial DNA was involved.” The work was interesting, but after 2 years, when his adviser left Yale, Lambowitz began looking for a new laboratory home. He joined Carolyn Slayman’s group, because she was also studying mitochondrial mutants and electron transport in another fungus, N. crassa.

“This was a fortuitous switch, ” notes Lambowitz, “because this was a very good time to be studying these kinds of mutants. Oxidative phosphorylation was the major biochemical problem of its day. All of the greatest biochemists were involved in investigating it.” Lambowitz spent much time comparing electron transport and oxidative phosphorylation between wild-type fungi and the mutant poky (2, 3). “Poky was one of the first mitochondrial mutants discovered. It’s a classical and mysterious mutant since it displays many different defects, ” he says.

Lambowitz also became interested in alternative oxidase, an enzyme responsible for cyanide-resistant respiration that was related to the mitochondrial mutants he was studying. After receiving his Ph.D. in 1972, Lambowitz moved to the Johnson Research Foundation at the University of Pennsylvania (Philadelphia) to start a 1-year postdoctoral position with the discoverer of alternative oxidase, Walter Bonner. Lambowitz also worked on a project investigating b-cytochromes in plant mitochondria. “The results of that project showed a then-popular theory of oxidative phosphorylation was incorrect, ” he says, “and probably helped cement the ascendancy of Peter Mitchell and chemiosmotic coupling” (4).

In 1973, Lambowitz moved on to The Rockefeller University (New York) to work with David Luck, one of the codiscoverers of mitochondrial DNA. “David was then working on characterizing the different components of the mitochondrial genetic system, and I went there with the goal of finding out the primary defect in poky that accounted for all the other observed defects, ” he says. While studying with Luck, Lambowitz made an unexpected finding when he discovered that part of the mitochondrial DNA encoded a ribosomal protein (5). “This was a first. Before that it was dogma that the only proteins encoded by mitochondrial DNA were components of the electron transport system, ” says Lambowitz.

Molecular Fossil Graveyards

After a brief fellowship at the National Institute of Mental Health (Bethesda), Lambowitz accepted his first faculty position in 1976 in the Department of Biochemistry at Saint Louis University School of Medicine (St. Louis). “The chairman, Robert Olson, gave me an excellent start-up package that enabled me to build a lab with four people almost at day one, ” he recalls, “which was fortunate. Jobs were scarce at the time. The NIH was going through the first of many periodic cutbacks, and there was no biotechnology industry.” Lambowitz was also fortunate because Luck had already begun changing the focus of his laboratory from mitochondrial genetics to studying flagella in Chlamydamonas. “When I left Luck’s lab, I was the last person still working on Neurospora, so when I moved to St. Louis I took the entire project with me, ” he says.

In St. Louis, Lambowitz was joined by Carmen Mannella, a friend from the Johnson Foundation, as well as graduate students Bob LaPolla and Rick Collins. With his new laboratory in place, Lambowitz resumed his quest to find the mitochondrial defect associated with the poky mutant. He was helped by David Perkins, a researcher at Stanford University (Stanford, CA) who had amassed a large collection of natural Neurospora strains. “He went out and isolated these strains from all over the world, many from places where it’s no longer possible for Americans to go safely, ” says Lambowitz of Perkins. Lambowitz wanted to use these different strains to develop physical markers for recombination experiments so he could map the poky mutation in the mitochondrial genome. When he investigated these natural strains, though, he made another unusual and unexpected find: some of the mitochondria harbored plasmid DNA in addition to their own DNA (6, 7).

Although Lambowitz found his research once again veering off its intended path, he did not forget about his original goals when obtaining the natural strains from Perkins. Eventually, Lambowitz figured out that the primary defect in poky was a 4-bp deletion at the 5′ end of the mitochondrial small rRNA (8), “although by the time we did that the finding was probably no longer of paramount interest, ” he says, “but we try to stick with problems until they’re solved.”

In 1986, Lambowitz was recruited by friend and collaborator Phil Perlman to take up a position as Ohio Eminent Scholar and Professor of Molecular Genetics and Biochemistry at Ohio State University (Columbus, OH). Here Lambowitz carried out biochemical analyses to elucidate the nature of these mitochondrial plasmids. “With Frank Nargang, we sequenced these plasmids, and it turned out that they encoded a reverse transcriptase, the same enzyme found in retroviruses, ” he says, “and, interestingly, it turned out to be an enzyme with unique biochemical properties. It’s the only enzyme that can initiate DNA synthesis de novo without a primer” (9).

“Fungal mitochondria are like a fossil graveyard, since things that are streamlined away in other systems are maintained apparently because there’s little selective pressure to get rid of them, ” says Lambowitz. He speculated that this unusual enzyme might be related to the first reverse transcriptases that evolved during the transition from an RNA to a DNA world billions of years ago. “It was like finding an island where dinosaurs still exist, ” he says.

“Fungal mitochondria are like a fossil graveyard…It was like finding an island where dinosaurs still exist.”

Splice of Life

Although Lambowitz arrived at Saint Louis University with the intention of continuing his own projects, he would soon find himself involved in others’ projects as well. Thad Pittenger, an established Neurospora geneticist, invited Lambowitz to give a seminar at Kansas State University (Manhattan, KS). “When I went out there, [Pittenger] told me that he was getting out of Neurospora research and going to work on plants. Pittenger had isolated many mutants in nuclear genes that affected mitochondrial processes, and he asked me if I wanted his collection of mutants. Of course, I immediately said yes, ” recalls Lambowitz. He received additional mutants from Helmut Bertrand, who had been a student of Pittenger’s, and the two went on to be friends and collaborators.

Back in St. Louis, Lambowitz and his group screened the newly acquired mutants for defects in mitochondrial ribosome assembly and found many with intriguing phenotypes, such as some affecting ribosomal RNA processing. Around this time, genes in eukaryotes were found to be discontinuous, with introns that were removed by RNA splicing. “Once splicing was discovered, we realized that our assembly mutants actually affected the splicing of the mitochondrial large ribosomal RNA (10). One of the mutant genes encoded a tyrosyl-tRNA synthetase, which is dually functional, and another encodes a DEAD-box protein, and we continue to work on these proteins to this day, ” says Lambowitz.

Those first mutants propelled Lambowitz toward a long research path studying the mechanics of intron splicing. Over the next few years, as researchers uncovered different types of introns, Lambowitz concentrated on two types: catalytic group I and group II introns. These two groups are present mainly in bacteria and mitochondria and chloroplasts of fungi and plants, and, unlike introns in higher organisms, they are self-splicing. Lambowitz also showed that group II introns encoded a reverse transcriptase, like that encoded by the ancient mitochondrial plasmids, and that this encoded enzyme possessed the dual function of helping the RNA fold into the active conformation (11).

Lambowitz has been especially fascinated with a feature unique to group II introns: their activity as mobile genetic elements. “We became interested in how the introns moved around from one place to another in genomes, ” he says, “and it turned out to be a novel and surprising mechanism that nobody imagined existed.” By both biochemical and genetic means, Lambowitz and Perlman demonstrated that the mobility intermediate was in fact the excised intron (12). “It uses its innate catalytic ability to just insert itself directly into one strand of a target DNA site, ” says Lambowitz, “then the associated reverse transcriptase cuts the opposite strand and makes a DNA copy of the inserted intron RNA.”

After elucidating the sequence elements involved in mobility, Lambowitz focused on using these introns as gene targeting vectors that could be reprogrammed to insert into any given site. Collaborating with Marlene Belfort and Gary Dunny, Lambowitz developed an in vivo expression system in E. coli using Ll.LtrB, an intron found in the fermenting bacteria Lactococcus lactis. He adapted the intron’s machinery to work in other bacteria and higher organisms, including designing an intron that could insert into HIV-1 proviral DNA and remain active inside human cells (13). Says Lambowitz, “The introns work very efficiently for gene targeting in bacteria, and we’re trying to get them to work equally efficiently in higher organisms. If we can do that, the introns could be very useful for functional genomics, with advantages over RNAi, and possibly even for gene therapy. So this might be the first practical thing I’ve ever done.”

An Inmate Running the Institute

In 1997, Lambowitz moved to Austin, TX, to become the director of the newly formed Institute for Cellular and Molecular Biology. The goal of the institute was to create an attractive scientific environment for conducting research in a university setting that would also impact education. Says Lambowitz, “The environment here is very investigator-driven. We’ve tried to design a setting where faculty are able to do their research efficiently, with minimal hindrances, and in a way that contributes to the undergraduate experience, since students can get taught by people who are excited about doing research and providing research opportunities. In some ways, it’s an experiment in whether the inmates can run the asylum.”

So far, Lambowitz has helped recruit more than 40 new faculty members investigating many aspects of molecular biology, particularly RNA research. “RNA is certainly an area of emphasis here, but it’s not the only area of emphasis, ” he says. The quantity and quality of graduate students has also risen during this same time. Although more remains to be done, including more faculty hiring, Lambowitz thinks the Institute for Cellular and Molecular Biology is on its way to becoming one of the top research programs in the United States. “The upward trajectory here has been pretty steep, ” he says, “and it is my ambition to keep it that way.”