PROFILE Profile of Susan S. Golden

Sujata Gupta Science Writer

Susan Golden did not set out to become Golden pursued other passions. She loved an expert in biological clocks, the internal literature, she says, an interest gleaned timepieces that keep life on Earth adjusted from her mother, an avid reader. And she to a 24-hour cycle. Instead, Golden, elected played the bassoon in the school band— in 2010 to the National Academy of Sci- where she made most of her friends. “That ences, wanted to identify the genes that un- turned out to be a social bifurcation. I did derpin . However, her focus not realize that the band route is the nerd changed in 1986 with the discovery of route. You can’t break over into the other biological clocks in (1). [cool] group,” Golden says. She also worked Because cyanobacteria are among Earth’s on the school newspaper as a photographer, earliest living organisms, the discovery made one, she is quick to note, without any formal clear that biological clocks are evolutionarily training. By the time she graduated high ancient. Golden had been studying photosyn- school in 1976 as salutatorian of her 600- thesis in cyanobacteria since graduate school. student class, Golden harbored dreams of Her reason was simple: Cyanobacteria are becoming a photojournalist for Life maga- single-celled, and thus they are much easier zine or National Geographic. to manipulate in a laboratory than plants. Golden’s main consideration in selecting a With her expertise in cyanobacteria, Golden college, though, was not prestige or program found herself well-positioned to identify the of study but money. By this point, Golden’s genes and that make the clock tick. parents were divorced and her mother “Cyanobacteria are present in niches and shouldered her expenses. “When I found Susan S. Golden. habitats all over the planet,” she says. out how much my mother made, I was “They’re very good at adapting to their shocked by how poor we were,” Golden habitat and that adaptation involves doing says. So when Mississippi University for wanted to perform molecular re- things at the right time.” Their timekeeping Women in Columbus offered her a place, search. So Golden joined the laboratory ability, she adds, helps cyanobacteria gen- Golden welcomed the opportunity. How- of Lou Sherman, who had earlier invited erate about 30% of atmospheric oxygen. ever, after only a day of classes, Golden her to enter UMC. Over the years, Golden and her collabo- realized that she didn’t want to be a jour- Besides providing her with academic focus, rators have revealed that the clock in cyano- nalist. Instead, Golden found herself loving graduate school brought Golden another surprise: a husband. James Golden, another bacteria works like a mechanical clock, introductory biology and soon switched her ’ complete with oscillators, gears, and hands. major to biology with a minor in chemistry. NIH trainee, soon became Golden srole In her recent research, including her In- With several advanced placement credits model. Despite decades of running adja- augural Article, Golden has shown how from high school and packed course loads cent laboratories, only recently have their clock proteins interact to synchronize the in college, Golden graduated from college lines of research converged. When they internal clock with the external 24-hour in just 2 years, unsure of her future. For- moved to the University of California at cycle (2, 3). To Golden’s own surprise, this tunately, she was accepted into a PhD San Diego in 2008, says Golden, their lab- recent line of inquiry has taken her back to program at the University of Missouri- oratories joined forces in researching cya- fi ’ nobacteria’s potential as a biofuel. her roots in photosynthesis. Her ndings Columbia. She became one of the school s ’ ’ show that cyanobacteria don’t use sensory first trainees in a new cell and molecular In Sherman s laboratory, Golden scharge was to develop a genetic system that could be photoreceptors, proteins that convey light- biology training program funded by the fi related information into the body in mam- National Institutes of Health. used to nd the proteins that make up the mals, to set their clocks. Instead, cyanobacteria photosynthetic reaction center in cyano- bacteria. The approach relied on a strategy integrate the ability to tell time with their For the Love of Chloroplasts photosynthetic apparatus. In retrospect, says of identifying mutant photosynthesis pro- fi As an undergraduate student, Golden had teins that cause cells to become resistant to Golden, this nding makes sense: In the pro- eagerly followed a once-fervent debate about karyote’sworld,shesays,“If photosynthesis is like atrazine (5). Golden con- ’ whether or not to allow recombinant DNA tinued the work when she entered Robert running, the lights are on. It s daytime. If research to continue. Despite the potential ’ photosynthesis is not running, it’s dark.” Haselkorn s laboratory at the University to fundamentally alter the course of genetic of Chicago in Illinois in 1983. By then, research, many researchers feared that

An Unlikely Path to the Academy genetic engineering could inadvertently fi ’ This is a Pro le of a recently elected member of the National The roots of Golden s career in plant biology change innocuous microbes into pathogens Academy of Sciences to accompany the member’s Inaugural Article were not formed at an early age. Instead, (4). At Missouri, Golden realized that she on page 17765 in issue 44 of volume 109.

8758–8760 | PNAS | May 28, 2013 | vol. 110 | no. 22 www.pnas.org/cgi/doi/10.1073/pnas.1305064110 Downloaded by guest on September 25, 2021 PROFILE researchers had isolated the gene thought Golden’s work caught the attention of Carl to a 24-hour cycle? Ultimately, the work to be responsible for resistance, Johnson, a researcher at led to Golden’s suite of findings detailing but they could not genetically engineer chlo- Vanderbilt University in Nashville, Ten- how the clock and photosynthesis are in- roplasts to confirm their theory. Golden, nessee. Johnson wanted to know whether tertwined in cyanobacteria. however, was able to mutate the suspected Golden had ever studied circadian rhythms Golden knew that she could change time gene, psbA, and reinsert it into cyanobac- in cyanobacteria. Golden recalled that a zones in her cyanobacteria by exposing them teria. She then exposed the mutants to the graduate student of hers had noticed to constant light, followed by a pulse of herbicide and, sure enough, they withstood “funny oscillations” in gene expression of darkness. However, when Golden mutated the assault. “We could show ... that this re- cyanobacteria grown for several days. “We a gene called cikA, the dark pulse caused no ally is the herbicide resistance gene,” Golden might have actually seen some evidence of change (13). “If you don’t have CikA, you says (6). that,” Golden informed Johnson. She sent still have a pretty good clock, but you can’t The findings demonstrated that genetic him a strain of the luciferase-tagged cya- reset it,” Golden says. “The cells have per- manipulation is easy in cyanobacteria, mak- nobacteria, and Johnson, together with manent jet lag.” ing it a suitable . During her Takao Kondo, a researcher now at Nagoya Next, Golden analyzed the structure of postdoctoral fellowship in Chicago, when she University in Japan, observed biolumines- CikA, revealing that CikA contained a began studying gene regulation, Golden cence from the cyanobacteria increase domain that resembled another found that cyanobacteria housed a family during the day and drop at night. The domain in KaiA (14, 15). Golden realized of three psbA genes (7). The three genes cyanobacteria’s light production continued that KaiA might also play a fundamental coded for two forms of the protein, one to oscillate even outside the day-night cy- role in setting the clock. Golden found that mutated to confer resistance to the cle. The researchers were ecstatic. At first, that CikA and KaiA bind to quinones, mol- herbicide, and two that seemed to code for Golden failed to understand the excitement. ecules that carry electrons. In photosynthesis, the same protein. Why, Golden wondered, It didn’t take long, though, for Golden quinones have few electrons (oxidized) when did cyanobacteria house those redundant to become enamored of the world of cir- the lights are off but gain electrons (reduced) genes? Over the next several years her re- cadian biology. Johnson and Kondo ex- when the lights come on. Golden showed search group found that the genes encoding plained that they had fashioned the first that the state of quinones influences one form of the protein were expressed known bacterial system in which they KaiA activity: When oxidized, as is the only under high luminance and the other couldisolateandstudythecomponents case when cells go into the dark, KaiA dis- expressed only under low luminance (8). of the clock. The team published their lodges from KaiC—the master protein of Further analysis revealed that cells optimize findings in 1993, noting that the discovery the clock—and binds quinones, thus re- their physiology by using the more efficient of the clock in a could explain setting the clock. The clock behaves “just as version of the protein under low stress con- how biological clocks evolved (9). if you hit a light switch,” Golden says (2, 3). ditions and switching to the high-stress op- The three laboratories, joined by Masahiro The finding, laid out in Golden’sInaugural tion when conditions become unfavorable. Ishiura in Japan, began working together to Article, expands an earlier finding show- identify components of the clock. Kondo ing a regulatory relationship between KaiA Turning to Clocks developed a screening device to sift through and KaiC. KaiA stimulates KaiC to phos- When Golden accepted a faculty position thousands of cyanobacterial colonies with phorylate, or transfer a phosphate group to at Texas A&M University in College Station mutated clocks (10). The researchers iden- a protein from ATP, the cell’senergysource in 1986, she had no intention of studying tified mutants that miscounted a day as (15). By controlling that process with qui- biological clocks. “Iwasdefinitely not looking having less than 24 hours or more than none binding, KaiA can convey luminance- at the clock. I was studying the regulation of 24 hours, as well as mutants with no rhythm related information to KaiC. Additionally, photosynthesis genes by light,” she says. at all. Golden’s tools for the genetic manip- KaiC can sense the ratio of ATP/ADP, However, unwittingly, Golden discovered a ulation of cyanobacteria enabled the group which also changes when cells enter dark- sought-after method for studying the clock. to fix the mutants to reset the clock to a ness (16). “With these two different ways of Her laboratory, Golden says, was searching 24-hour cycle. That approach helped the sensing photosynthesis, the [KaiC] oscilla- for that caused the light regulation group identify three genes—kaiA, kaiB, and tor can sense both when the lights go off of photosynthesis genes to break down. kaiC—that code for oscillator proteins that and how long they’re off,” Golden says. To find such mutations, she needed a way keep the clock on time (11). Just as cyanobacteria don’t directly sense to measure gene expression in living cells. Golden then looked for secondary com- light via photoreceptors, the human body Such an approach would let her approxi- ponents of the clock, or proteins that in- has many organs that use clocks that don’t mate how much a gene is expressed under directly influence circadian rhythms. For rely on light. For instance, the liver sets its certain light conditions and how that ex- instance, Golden found that knocking out clock not through light but through feed- pression changes under other conditions. a gene called sasA threw the cyanobacte- ing. Perhaps these peripheral clocks work She could then identify mutants that failed rial clock out of kilter (12). SasA is critical like the clock in cyanobacteria and use to regulate properly. Golden attached the for relaying time-related information to energy transfers to stay synchronized, Golden genes she was studying to a luciferase gene, the rest of the cell, much like the hands of speculates. similar to the gene that causes fireflies to a clock that help us tell time, Golden says. light up. She then borrowed a night vision Finding the Clock’s Hands scope from a colleague and eyeballed her Return to Photosynthesis As Golden unravels the secrets underlying cyanobacteria. Sure enough, light emissions Before long, Golden began investigating how the clock, her questions have broadened. from the bacteria placed in the dark light-related information enters the clock. How, for instance, does the clock control the changed when the cells were first subjected How is it, she mused, that the cell reads timing of cell division? And how do cells to different intensities of light. cues in its environment to stay calibrated inherit a sense of time? Having established

Gupta PNAS | May 28, 2013 | vol. 110 | no. 22 | 8759 Downloaded by guest on September 25, 2021 how light-related information enters the at UCSD, where she now 8 Schaefer MR, Golden SS (1989) Light availability influences the clock, she now wants to determine how serves as director. ratio of two forms of D1 in cyanobacterial thylakoids. J Biol Chem 264(13):7412–7417. time-related information exits it. Besides investigating what makes the cya- 9 Kondo T, et al. (1993) Circadian rhythms in : Luciferase Golden’s research into the mechanisms nobacterial clock tick, Golden has begun as a reporter of circadian gene expression in cyanobacteria. Proc Natl of photosynthesis and the biological clock taking her research in a new direction. At Acad Sci USA 90(12):5672–5676. 10 has earned her accolades throughout her UCSD’s Center for Algae Biotechnology, Kondo T, et al. (1994) mutants of cyanobacteria. Science 266(5188):1233–1236. career, including a National Science Foun- Golden is helping to assess the feasibility 11 Ishiura MS, et al. (1998) Expression of a gene cluster kaiABC as a dation Presidential Young Investigator Award of using cyanobacteria as a biofuel. “Cya- circadian feedback process in cyanobacteria. Science 281(5382): from 1989 to 1995 and a fellowship in the nobacteria are already really good at con- 1519–1523. 12 American Academy of Microbiology in 2000. verting light energy to chemical energy. Iwasaki H, et al. (2000) A kaiC-interacting sensory histidine ’ ” kinase, SasA, necessary to sustain robust circadian oscillation in Golden also helped start the Center for That s what they do for a living, she says. cyanobacteria. Cell 101(2):223–233. 13 Schmitz O, Katayama M, Williams SB, Kondo T, Golden SS (2000) CikA, a bacteriophytochrome that resets the cyanobacterial circadian 1 Grobbelaar N, Huang T-C, Lin H-Y, Chow T-J (1986) Dinitrogen- 5 Golden SS, Sherman LA (1984) Biochemical and biophysical clock. Science 289(5480):765–768. 14 fixing endogenous rhythm in RF-1. FEMS Microbiol characterization of herbicide-resistant mutants of the unicellular Gao T, Zhang X, Ivleva NB, Golden SS, LiWang A (2007) NMR – Lett 37:173 177. cyanobacterium, Anacystis nidulans R2. BBA-Bioenergetics. 764(2): structure of the pseudo-receiver domain of CikA. Protein Sci 16(3): 2 Wood TL, et al. (2010) The KaiA protein of the cyanobacterial 239–246. 465–475. circadian oscillator is modulated by a redox-active cofactor. Proc Natl 6 Golden SS, Haselkorn R (1985) to herbicide resistance 15 Williams SB, Vakonakis I, Golden SS, LiWang AC (2002) Structure Acad Sci USA 107(13):5804–5809. maps within the psbA gene of Anacystis nidulans R2. Science and function from the circadian clock protein KaiA of Synechococcus 3 Kim YI, Vinyard DJ, Ananyev GM, Dismukes GC, Golden SS 229(4718):1104–1107. elongatus: A potential clock input mechanism. Proc Natl Acad Sci (2012) Oxidized quinones signal onset of darkness directly to 7 Golden SS, Brusslan J, Haselkorn R (1986) Expression of – the cyanobacterial circadian oscillator. Proc Natl Acad Sci USA USA 99(24):15357 15362. 16 ’ 109(44):17765–17769. afamilyofpsbA genes encoding a photosystem II polypeptide in Rust MJ, Golden SS, O Shea EK (2011) Light-driven changes 4 Berg P, Singer MF (1995) The recombinant DNA controversy: the cyanobacterium Anacystis nidulans R2. EMBO J 5(11): in energy metabolism directly entrain the cyanobacterial Twenty years later. Proc Natl Acad Sci USA 92(20):9011–9013. 2789–2798. circadian oscillator. Science 331(6014):220–223.

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