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Kary Mullis e la PCR

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Un articolo del 2021 comparso sulla rivista National Geographic riassume la storia dell’invenzione e soprattutto dell’inventore della PCR, tecnica alla base di moltissimi studi ed applicazioni di biologia molecolare.

“The simple technique would make as many copies as I wanted of any DNA sequence I chose, and everybody on Earth who cared about DNA would want to use it,” Mullis recounts in his colorfully titled 1998 memoir Dancing Naked in the Mind Field.

If you start with just one piece of DNA, you’ll have two copies of your target sequence after one PCR cycle. Each copy can again be unwound to make more templates. After just 30 cycles, you’ll have over a billion copies—all from one molecule of DNA.

Lo scienziato dietro scoperta della PCR, che gli valse il premio Nobel per la chimica, fu Kary Mullis, figura eccentrica e dalle opinioni controverse (negazionista del legame HIV-AIDS, scettico sul cambiamento climatico e sui composti responsabili del buco dell’ozono). L’articolo descrive anche i contrasti che nacquero tra Mullis e il resto del team di scienziati che lavorava sulla tecnica alla Cetus Corporation, una delle prime compagnie di biotecnologie al mondo.

White still reminisces about his unquestionable creativity, sharp wit, and good humor—but laments how the myth took over the man. “Mullis rejected all of his former friends and colleagues and just disparaged us,” he says. “The Nobel Prize went to his head.”

In questo articolo di Scientific American del 1990, Kary Mulllis racconta il momento in cui l’idea alla base della PCR gli balenò in testa, come una rivelazione, e i dettagli della tecnica.

…such a revelation came to me one Friday night in April, 1983, as I gripped the steering wheel of my car and snaked along a moonlit mountain road into northern California’s redwood country.

Per chi fosse interessato a sapere di più della tumultuosa carriera e vita privata di Kary Mullis, proponiamo il coccodrillo di California, la visita degli alumni della Università della California Berkeley dal titolo “Intolerable Genius: Berkeley’s Most Controversial Nobel Laureate“:

He fought with his bosses. He fought with his coworkers. He fought with Cetus security guards and receptionists. Though married, he dated his labmates—and fought with them, too. Behind Mullis’s bellicosity seemed to be an abiding certainty that he was brilliant and everyone else was a fool, hell-bent on undermining his work. Cetus management was left wondering: What do we do with this guy?

Mullis was notorious at Berkeley for his irreverent approach to science and his skill in synthesizing psychedelic drugs. His curiosity ranged far beyond chemistry. At 22, he sent off an article to the prestigious journal Nature describing, in his words, “the entire universe from beginning to end.”

Dopo aver dimostrato che la sua idea per moltiplicare il DNA funzionava, Mullis abbandonò la Cetus Corp. e la scienza, ed iniziò a nutrire rancore verso i colleghi e la comunità scietifica in generale. La maggior parte del suo tempo Mullis lo dedicava al surf, ma nel 19965 accettò di partecipare come esperto per la difesa al processo contro O.J. Simpson, il suo ruolo sarebbe stato quello di screditare le prove sul DNA (la difesa però decise di non farlo deporre).

…If the O.J. Simpson chapter of Mullis’s post-Nobel life was odd, it was only in keeping with the rest of it. He’d largely given up professional science and, along with surfing, had taken up roller-skating, playing the guitar, and studying astrology. He cofounded a company called StarGene, which planned to sell jewelry with the DNA of dead celebrities embedded inside. “I’m not a ‘serious’ genius like Einstein,” he told the Los Angeles Times. “I’m a more playful kind of genius.”

…One night in 1985, as Mullis took a stroll on his property in Mendocino County, he encountered a glowing raccoon.

“Good evening, doctor,” the raccoon said.

The next thing Mullis remembered he was walking along a nearby road in the light of morning, a time gap he attributed to alien abduction. He detailed the encounter in his memoir, Dancing Naked in the Mind Field.

Un podcast dei New England Biolabs parla invece in maggior dettaglio dello sviluppo della tecnica e dell’importanza dell’enzima taq DNA polymerase:

Early PCR required a person to stand by and add DNA polymerase called the Klenow fragment with each cycle because the high temperatures that you needed earlier in the cycle to pull that double-stranded DNA apart would heat and activate, or kill, the polymerase. Standing by and manually adding fresh enzyme in every cycle became very, very tedious. It quickly became clear that what was needed was an enzyme that could handle the high temperatures of PCR. Where better to look for such an enzyme than in the bacteria that normally grow in very hot areas of our planet?

As luck would have it, earlier in 1969, a scientist named Tom Brock was working on understanding how living bacterial cells managed to survive and thrive at extreme temperatures like those in the hot springs of Yellowstone. In these hot springs, he discovered a bacterium called Thermus aquaticus, which translates to “living in hot water.”

In 1976, another scientist named Alice Chen isolated and characterized, on a small scale, the enzyme that would come to be called taq DNA polymerase. And that polymerase could tolerate temperatures up to 95 degrees C, very close to boiling water temperatures, perfect for PCR, although it hadn’t been discovered by Kary yet. It was just very fortunate that when PCR did come along, taq DNA polymerase was waiting in the wings, so to speak. The PCR-driven need for a thermostable enzyme focused attention fast on the potential of taq.

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