Copyright 1998 by the Genetics Society of America
Perspectives
Anectdotal, Historical and Critical Commentaries on Genetics
Edited by James F. Crow and William F. Dove
Hershey
Franklin W. Stahl
Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403-1229
ALFRED Day Hershey died at his home, in the Village arriveultimately at some correlation between thechemical constitution of [Brucella species], and the various phe-of Laurel Hollow, New York, on May 22, 1997 at the age of 88. Seven weeks later, a number of Al’s friends met nomena of specificity by them” (Hershey 1934). Al then assumed an instructorship in Bacteriology andat Cold Spring Harbor to commemorate his life. The tributes paid on that occasion have informed this Perspec- Immunology at Washington University in St. Louis, where he collaborated with Professor J. Bronfenbrenner. Fromtives , and some of them are cited in what follows. Full copies are available from the Cold Spring Harbor La- 1936 to 1939, their papers reported studies on the growth of bacterial cultures. Al certainly had the backgroundboratory. Most students of biology know of Hershey—his best for this work; his thesis research had involved not only the preparation of liver infusion growth medium (fromknown experiment is described in texts of both biology and genetics. This work (Hershey and Chase 1952a) scratch, as was routine in those days) but also the testing of 600 better defined media, none of which supportedprovided cogent support for the hypothesis that DNA is the conveyor of genetic information. growth of Brucella. From 1940 to 1944, his experiments dealt withthephage-antiphageimmunologic reactionandThe subject of the “Hershey-Chase experiment” was the bacteriophage T2, composed half of protein and half of withotherfactorsthat influencedphage infectivity.During both those periods, about half of the 28 papers bearingDNA, a combination compatible with any of the three competing views of the chemical basis of heredity. T2, like Hershey’s name were sole-authored. (It was apparently here that Al learned how to handle phage. It may alsomany other phages, is a tadpole-shaped virus that initiates an attack on a bacterium by sticking to it with the tip of have been here that Al acquired the idea that authorship belongs to those who do the experiments and should notits tail. The Hershey-Chase experiment used DNA-specific and protein-specific radioactive labels to show that the reflect patronization, rank, title, or even redaction of the manuscript.) Some of these papers may have been impor-DNA of the virus then entered the bacterium while most of the protein could be stripped from the surface of the tant contributions to the understanding of antigen-antibody reactions. To this reviewer they appear original,cell by agitation in a Waring Blender. Such abused cells produced a normal crop of new phage particles. Previous thoughtful, and quantitative, especially those on the use of phage inactivation to permit the study of the antigen-evidence implicating DNA in heredity had shown that a property of the surface coat of the pneumococcus bacte- antibody reaction at “infinite” dilution of antigen (e.g.,
Hershey 1941). But, of course, they interested an audi-rium couldbepassedfromonestrainto anotherviachemically isolated DNA. The observation by Hershey and ence that did not include many geneticists or others interested in biological replication (except, perhaps, for LinusChase justified the view that the entire set of hereditary information of a creature was so encoded. This work Pauling). It took Max Delbru ¨ ck to move Al in that direction.countedheavilyinmaking Hershey a shareholder, with
Max Delbru ¨ ck (1906–1981) and Salvadore E. Luria As recounted by Judson (1996), Delbru ¨ck was attracted by Al’s papers. Perhaps he liked their mathemati-(1912–1991), of the 1969 Nobel prize for Physiology or Medicine. cal, nonbiochemical nature. He must have liked their originality, logical precision, and economy of presenta-In 1934, Al earned his Ph.D. in the Departments of Chemistry andBacteriology at Michigan StateCollegewith tion. Max invited Al to Nashville in 1943 and recorded the following impression: “Drinks whiskey but not tea.a thesis that described separations of bacterial constituents, identified by the quaint definitions of the times. Simple and to the point . . . Likes independence.” Al’s first “interesting” phage papers appeared soon thereafterExcept for its evident care and industry, the work was unremarkable, merely part of an ongoing study “. . . to (Hershey 1946, 1947).
Genetics 149: 1–6 (May, 1998)
2 F. W. Stahl
A sine qua non for genetical investigation is the availabil- quent to their formation. Delbru ¨ ck stopped thinking about phage genetics after Charley Steinberg and Iity of mutants. The ease with which large numbers of phage particles can be handled facilitated the discovery (1958) showed him that his final expressions were independent of both of his two assumptions, reciprocal andand characterization of mutants that were easily scored. Al recognized that the high infectivity of phage and the break-join. A fully satisfactory conclusion to these issues for T2 came only with Mosig’s and Albert ’s elucidationproportionality of plaque count to volume of suspension assayed allowed for quantification of mutation far ex- of the nonreciprocal, replicative mechanism by which recombinants are formed in T-even phages (for review, seeceeding that possible in most other viral systems. Al measured mutation rates, both forward and back, and demon- Mosig 1994). More recent advances have established that the various recombinational mechanisms employed bystrated the mutational independence of r (rapidlysis) and h (host range). He succeeded also in showing (in parallel bacteria and their viruses and by eukaryotes are, in fact, pleasingly similar, depending on homologous strategieswith Delbru ¨ ck) that these mutationally independent factors could recombine when two genotypes were grown and enzymes. By most criteria, individual T2 particles are “haploid”—together in the same host cells ( Hershey 1946, 1947). Thus, “Phage Genetics” was born as a field of study, and they contain but one set of genetic material. However, “heterozygous” particles, which contain two different al-it became conceivable not only that the basic question of biological replication could be addressed with phage but leles at a single locus, were described by Hershey and
Chase (1952b) at the 1951 Cold Spring Harbor Sympo-so could phenomena embraced by the term “MorganMendelism.” sium. After the elucidation of DNA as a duplex molecule (Watson and Crick 1953), it was possible to proposeAl continued the formal genetic analyses of T2 with investigations of linkage. Hershey and Rotman (1948) heteroduplex models for those “heterozygotes.” Such models played a central role in all subsequent thinkingdemonstratedthat linkage analysis would have to take into account the production of recombinant particles con- about recombination, especially that involving relationships between meiotic crossing over and gene conversion.taining markers from three different infecting phage genotypes. Thesameauthors(1949)used“mixedindicators” In 1958, Hershey, like Levinthal (1954) before him, expanded onthe Visconti-Delbru ¨ ck analysis in an effortto enumerate all four genotypes from two-factor crosses involving h and r mutants. That trick made it feasible to to connect observations on heterozygotes, which had molecular implications, with formal concepts proposed toanalyze fully the yields from individual mixedly infected bacterial cells. The signal finding was that all four geno- deal with the populational aspects of phage crosses. The effort providedfew, if any, answers, but clarified the ambi-types of phage could be produced by an individual cell but that the numbers of complementary recombinants, ent questions, at least for Al. In 1950, Al left St. Louis to join the staff of the Carnegiewhich were equal on the average, showed little correlation from cell to cell. This demonstration of apparent nonre- Institution of Washington at Cold Spring Harbor. That move put himat thegeographicalcenter ofthe embryonicciprocality in the exchange process leading to recombination raisedthespecterthat“crossing over” inphageswould field of microbial/molecular genetics, and he soon became the intellectual center of its phage branch. At thisprove to be fundamentally different from that occurring in meiosis. The desire to unify this and other apparently time, the fruits of a collaboration conducted at St. Louis were published (Hershey et al. 1951). This work showeddisparate properties of phage and eukaryotic recombination into a single theoretical framework motivated subse- that phage particles were “killed” by the decay of the unstable isotope 32 P incorporated within their DNA. Afterquent studies of recombination by other investigators.
Delbru ¨ck tried to make such aunification by algebraic the central importance of DNA to the phage life cycle (and to genetics) had been demonstrated, this “suicide”legerdemain and Papal Bull (see below). He formalized phage recombination as a succession of meiosis-like, pair- technique was exploited in other labs in efforts to analyze the phage genetic structure and its mode of replication.wise exchanges between linear linkage structures ( Visconti and Delbru ¨ ck 1953). The resulting algebra em- Likemost earlyexperimentsin“radiobiology,” theseanalyses were fun but not much more. From this time on, Al’sbracedsomeofthemajorwaysinwhichphagelinkagedata differed from meiotic data. In particular, it rationalized studies became more down-to-earth (and successful) as he turned from mathematically based genetic analyses tothe “negative interference” between crossovers and the appearance of progeny particles that had inherited mark- serious studies of phage structure and the biochem
Copyright 1998 by the Genetics Society of America
Perspectives
Anectdotal, Historical and Critical Commentaries on Genetics
Edited by James F. Crow and William F. Dove
Hershey
Franklin W. Stahl
Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403-1229
ALFRED Day Hershey died at his home, in the Village arriveultimately at some correlation between thechemical constitution of [Brucella species], and the various phe-of Laurel Hollow, New York, on May 22, 1997 at the age of 88. Seven weeks later, a number of Al’s friends met nomena of specificity by them” (Hershey 1934). Al then assumed an instructorship in Bacteriology andat Cold Spring Harbor to commemorate his life. The tributes paid on that occasion have informed this Perspec- Immunology at Washington University in St. Louis, where he collaborated with Professor J. Bronfenbrenner. Fromtives , and some of them are cited in what follows. Full copies are available from the Cold Spring Harbor La- 1936 to 1939, their papers reported studies on the growth of bacterial cultures. Al certainly had the backgroundboratory. Most students of biology know of Hershey—his best for this work; his thesis research had involved not only the preparation of liver infusion growth medium (fromknown experiment is described in texts of both biology and genetics. This work (Hershey and Chase 1952a) scratch, as was routine in those days) but also the testing of 600 better defined media, none of which supportedprovided cogent support for the hypothesis that DNA is the conveyor of genetic information. growth of Brucella. From 1940 to 1944, his experiments dealt withthephage-antiphageimmunologic reactionandThe subject of the “Hershey-Chase experiment” was the bacteriophage T2, composed half of protein and half of withotherfactorsthat influencedphage infectivity.During both those periods, about half of the 28 papers bearingDNA, a combination compatible with any of the three competing views of the chemical basis of heredity. T2, like Hershey’s name were sole-authored. (It was apparently here that Al learned how to handle phage. It may alsomany other phages, is a tadpole-shaped virus that initiates an attack on a bacterium by sticking to it with the tip of have been here that Al acquired the idea that authorship belongs to those who do the experiments and should notits tail. The Hershey-Chase experiment used DNA-specific and protein-specific radioactive labels to show that the reflect patronization, rank, title, or even redaction of the manuscript.) Some of these papers may have been impor-DNA of the virus then entered the bacterium while most of the protein could be stripped from the surface of the tant contributions to the understanding of antigen-antibody reactions. To this reviewer they appear original,cell by agitation in a Waring Blender. Such abused cells produced a normal crop of new phage particles. Previous thoughtful, and quantitative, especially those on the use of phage inactivation to permit the study of the antigen-evidence implicating DNA in heredity had shown that a property of the surface coat of the pneumococcus bacte- antibody reaction at “infinite” dilution of antigen (e.g.,
Hershey 1941). But, of course, they interested an audi-rium couldbepassedfromonestrainto anotherviachemically isolated DNA. The observation by Hershey and ence that did not include many geneticists or others interested in biological replication (except, perhaps, for LinusChase justified the view that the entire set of hereditary information of a creature was so encoded. This work Pauling). It took Max Delbru ¨ ck to move Al in that direction.countedheavilyinmaking Hershey a shareholder, with
Max Delbru ¨ ck (1906–1981) and Salvadore E. Luria As recounted by Judson (1996), Delbru ¨ck was attracted by Al’s papers. Perhaps he liked their mathemati-(1912–1991), of the 1969 Nobel prize for Physiology or Medicine. cal, nonbiochemical nature. He must have liked their originality, logical precision, and economy of presenta-In 1934, Al earned his Ph.D. in the Departments of Chemistry andBacteriology at Michigan StateCollegewith tion. Max invited Al to Nashville in 1943 and recorded the following impression: “Drinks whiskey but not tea.a thesis that described separations of bacterial constituents, identified by the quaint definitions of the times. Simple and to the point . . . Likes independence.” Al’s first “interesting” phage papers appeared soon thereafterExcept for its evident care and industry, the work was unremarkable, merely part of an ongoing study “. . . to (Hershey 1946, 1947).
Genetics 149: 1–6 (May, 1998)
2 F. W. Stahl
A sine qua non for genetical investigation is the availabil- quent to their formation. Delbru ¨ ck stopped thinking about phage genetics after Charley Steinberg and Iity of mutants. The ease with which large numbers of phage particles can be handled facilitated the discovery (1958) showed him that his final expressions were independent of both of his two assumptions, reciprocal andand characterization of mutants that were easily scored. Al recognized that the high infectivity of phage and the break-join. A fully satisfactory conclusion to these issues for T2 came only with Mosig’s and Albert ’s elucidationproportionality of plaque count to volume of suspension assayed allowed for quantification of mutation far ex- of the nonreciprocal, replicative mechanism by which recombinants are formed in T-even phages (for review, seeceeding that possible in most other viral systems. Al measured mutation rates, both forward and back, and demon- Mosig 1994). More recent advances have established that the various recombinational mechanisms employed bystrated the mutational independence of r (rapidlysis) and h (host range). He succeeded also in showing (in parallel bacteria and their viruses and by eukaryotes are, in fact, pleasingly similar, depending on homologous strategieswith Delbru ¨ ck) that these mutationally independent factors could recombine when two genotypes were grown and enzymes. By most criteria, individual T2 particles are “haploid”—together in the same host cells ( Hershey 1946, 1947). Thus, “Phage Genetics” was born as a field of study, and they contain but one set of genetic material. However, “heterozygous” particles, which contain two different al-it became conceivable not only that the basic question of biological replication could be addressed with phage but leles at a single locus, were described by Hershey and
Chase (1952b) at the 1951 Cold Spring Harbor Sympo-so could phenomena embraced by the term “MorganMendelism.” sium. After the elucidation of DNA as a duplex molecule (Watson and Crick 1953), it was possible to proposeAl continued the formal genetic analyses of T2 with investigations of linkage. Hershey and Rotman (1948) heteroduplex models for those “heterozygotes.” Such models played a central role in all subsequent thinkingdemonstratedthat linkage analysis would have to take into account the production of recombinant particles con- about recombination, especially that involving relationships between meiotic crossing over and gene conversion.taining markers from three different infecting phage genotypes. Thesameauthors(1949)used“mixedindicators” In 1958, Hershey, like Levinthal (1954) before him, expanded onthe Visconti-Delbru ¨ ck analysis in an effortto enumerate all four genotypes from two-factor crosses involving h and r mutants. That trick made it feasible to to connect observations on heterozygotes, which had molecular implications, with formal concepts proposed toanalyze fully the yields from individual mixedly infected bacterial cells. The signal finding was that all four geno- deal with the populational aspects of phage crosses. The effort providedfew, if any, answers, but clarified the ambi-types of phage could be produced by an individual cell but that the numbers of complementary recombinants, ent questions, at least for Al. In 1950, Al left St. Louis to join the staff of the Carnegiewhich were equal on the average, showed little correlation from cell to cell. This demonstration of apparent nonre- Institution of Washington at Cold Spring Harbor. That move put himat thegeographicalcenter ofthe embryonicciprocality in the exchange process leading to recombination raisedthespecterthat“crossing over” inphageswould field of microbial/molecular genetics, and he soon became the intellectual center of its phage branch. At thisprove to be fundamentally different from that occurring in meiosis. The desire to unify this and other apparently time, the fruits of a collaboration conducted at St. Louis were published (Hershey et al. 1951). This work showeddisparate properties of phage and eukaryotic recombination into a single theoretical framework motivated subse- that phage particles were “killed” by the decay of the unstable isotope 32 P incorporated within their DNA. Afterquent studies of recombination by other investigators.
Delbru ¨ck tried to make such aunification by algebraic the central importance of DNA to the phage life cycle (and to genetics) had been demonstrated, this “suicide”legerdemain and Papal Bull (see below). He formalized phage recombination as a succession of meiosis-like, pair- technique was exploited in other labs in efforts to analyze the phage genetic structure and its mode of replication.wise exchanges between linear linkage structures ( Visconti and Delbru ¨ ck 1953). The resulting algebra em- Likemost earlyexperimentsin“radiobiology,” theseanalyses were fun but not much more. From this time on, Al’sbracedsomeofthemajorwaysinwhichphagelinkagedata differed from meiotic data. In particular, it rationalized studies became more down-to-earth (and successful) as he turned from mathematically based genetic analyses tothe “negative interference” between crossovers and the appearance of progeny particles that had inherited mark- serious studies of phage structure and the biochem
การแปล กรุณารอสักครู่..