Perennial Prescience

At a gathering last summer overlooking Little Harbor in WoodsHole,Massachusetts, a group of friends celebrated the 97th birthday of the extraordinary American biochemist Arthur Pardee (Fig. 1). As he and I chatted, covering many things, I got to thinking of the fact that, amid hismanymajor contributions tomolecularbiology, hewas remarkably prescient on at least three occasions: the experimental anticipation of messenger RNA, the discovery of enzyme allosteric regulation, and the initial insight of what later became known as cell cycle checkpoints. In both textbooks and the minds of many molecular biologists of the late 20th and early 21st centuries, the discovery of messenger RNA was made nearly simultaneously by groups at Caltech and Harvard in 1961 (1, 2). Those two publications are themselves quite a story, including an agreement by the Caltech group to withhold submission of their paper until theHarvard labwas ready todoso.Readersmayconsider this a remarkable factgiven theprofundityof thepapers, but the backstory is that there were close personal relationships and mutual admiration among key players in the two groups, most notably betweenMatthewMeselson and the visiting SydneyBrenner at Caltech on the one hand, and their compatriot Jim Watson at Harvard on the other. The plans for the Caltech experiments were cast in the spring of 1960 (Fig. 2), whereas the Harvard group was somewhat behind. Interested readers can pursue more on this elsewhere (3, 4). Both the Caltech and Harvard groups thought, correctly as it turned out, that phage-infected bacteria would be an ideal system to capture thepostulatedunstableRNA intermediate between the phage DNA and its protein products, as it was known that host-cell RNA synthesis is shut downafter phage infection, thus clearing the stage for the phage RNA to strut out for a solo performance (in the Caltech case adorned with a heavy isotope and thus revealedby isopycnicbanding inCsCl equilibriumdensity gradient centrifugation, and in the Harvard case associatingwith ribosomes in a sucrose gradient). But already in 1958, on a sabbatical visit to the Pasteur Institute, Pardee had opted to use a different strategy: the mating ritual of Escherichia coli strains in which the genetic information transfer involved in both the constitutive and inducible states of b-galactosidase synthesis could be related to the known DNA transfer that took place in such conjugation experiments but also, and this was key, the known noncytoplasmic transfer. These and other results Pardee obtained were consistent with the involvement of a nonDNA, unstable cytoplasmic element. Published first in 1958 along with other results of his Pasteur colleagues (5), Pardee published an account thereafter from a symposium (6). Both of these papers are, beyond the important findings reported, models of not only how to write a paper but also how to organize one’s thoughts in the first place. These findings anticipated the formal description of messenger RNA and were later published in a complete article (7), with the conjugation studies acquiring the acronym “PaJaMo experiment. ” The term caught on. Many buffers (e.g. Sorensen), bacterial growthmedia (e.g., Luria broth), ormammalian ones (e.g., Eagle medium), devices (e.g. Dounce homogenizer), and techniques (e.g. Sanger dideoxy DNA sequencing) carry the names of their inventors. But this was one of the first times an experimenthadbeennamed for the investigators, although, ironically, this was co-contemporaneous with another case, theMeselson-Stahl experiment revealing the semiconservative replicationofDNA(8). It is also amusing toponder that, given the tremendous intensityof thework, it is not clear if Pardee, Jacob, andMonod ever had time to slip into pajamas for a few hours of sleep before running back to the lab a few hours later. The second case of Pardee’s prescience relates to allostery, which I regard as the second greatest discovery in the modern era of biochemistry (I have stated this often in various learned company, and, so far, noonehasbittenmy head off). The idea that enzymes can be regulated by feedback inhibition (or activation) by the concentration of a product had been established by Edwin Umbarger, but howthisworkedwasamysteryat the time, althoughwork on the cooperativity of oxygen:hemoglobin binding by Jeffries Wyman and John Edsall had set the stage, albeit with a nonenzyme. Working on this problem of feedback