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Joshua Lederberg1925 – 2008

Norton Zinder1928 – 2012

Discovered that bacteriophage can carry genes from on bacterium to another.Initial experiments were carried out in Salmonella. Lederberg and Zinder named this process transduction.

Discovery of transduction

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1 .Started with phe-, trp-, tyr- and met-, his-, from the bacterium Salmonella typhimurium

2 .After the two strains were mixed wild type prototrophs appearedat the frequency of about 1 to 105 (similar to E. coli)

3 .In this case the researchers also recovered recombinants from a U-tube experiment

4 .By varying the size of the pores in the filter, they found that theagent responsible for gene transfer was the same size as a known

phage of salmonella called phage P22

Discovery of transduction

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The researchers also recovered recombinants from a U-tube experiment

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Background: viral infection

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A generalized bacteriophage lytic cycle

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Micro -> Macro?With plaques.

Phage plaques

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I. Mapping phage chromosomes using phage crossesh-: can infect two different E.coli strains (strains 1 and 2)h+: can infect only strain 1r-: rapidly lyses cells, thereby producing large plaquesr+: slowly lyses cells, producing small plaques

Mixed infection

Strain 1 is infected with both parental T2 phage genotypes.After an appropriate incubation period, the phage lysate is then analysed by spreading it onto a bacterial lawn composed of a mixture of E. coli strains 1 and 2. 14

h clearness (here-

color) of plaquer size of plaque

1 .Large plaques indicate rapid lysis (r-)2 .Small plaques slow lysis (r+)

3 .Phage plaques with allele (h-) will infect both hosts, forming a clear plaque4 .Phage plaques with the allele (h+) can infect only strain 1, forming a cloudy plaque

h-r+ h+r-x

h-r+ h+r- h-r- h+r+

I. Mapping phage chromosomes using phage crosses

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I. Mapping the genome of a virus

RF= (h+ r+) + (h- r-) total plaques16

II. Transduction, and mapping of the Bacterial genome

The mechanism of generalized transduction

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IIa. Generalized Transduction

Score co-transductants , derive order and relative distance

thr azileu leuthraziOR

leuthr aziP1 can only cotransduce genes less then approximately 1.5 min apart on the E.coli chromosome map

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Virulent phage Temperate phage/prophage

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Specialized Transduction: Via a phage that integrates at ONE site

site-specific recombinationNOT homologous recombination

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IIa. Specialized Transduction: Via a phage that integrates at ONE site

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IIa. Specialized Transduction: Via a phage that integrates in one site

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F’ - duction

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F’

F-

F’-duction25

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The 1963 genetic map of E.coli.units are in minutes, based on interrupted-mating experiments

(position of approximately 100 genes)27

Linear scale drawing of a 5-minutes section of the 100-minute 1990 E.colilinkage map

(1990 ,total of more then 1400 genes)28

September 1997-The complete sequence of the E. coli genome

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Genetic map

Physical map (open reading frames – gene sequences)

Correlation of the genetic and physical maps

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Molecular Genetics

•First step: DNA is the genetic material

– DNA, NOT protein of the chromosomes/chromatin

–PROVEN WITH TRANSFORMATION AND TRANSDUCTION, THAT WE JUST MASTERED

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James D. Watson1928( age 84)

Francis Crick1916-2004

The Nobel Prize in Physiology or Medicine 1962 was awarded jointly to Francis Harry Compton Crick, James Dewey Watson and Maurice Hugh Frederick Wilkins "for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in

living material".

Maurice Wilkins1916-2004

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“We wish to suggest a structure for the the salt of deoxyribose nucleic acid (D.N.A)this structure has a novel features which are

of considerable biological interest”

Rosalind Franklin1920– 1958

X-rayDiffraction analysisOf DNA

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Ten years after Rosalind Franklin's death, James Watson in his best-selling book The Double Helix wrote that:

" By choice she did not emphasize her feminine qualities . . . .There was never lipstick to contrast with her straight black hair, while

at the age of thirty-one her dresses showed all the imagination of English blue-stocking adolescents. So it was quite easy to imagine her

the product of an unsatisfied mother who unduly stressed the desirability of professional careers that could save bright girls from marriages to dull men . . . .

Clearly Rosy had to go or be put in her place. The former was obviously preferable because, given her belligerent moods, it would be very

difficult for Maurice [Wilkins] to maintain a dominant position that would allow him to think unhindered about DNA . . . .

The thought could not be avoided that the best home for a feminist was in another person's lab”.

רוזי, כמובן, לא העבירה לנו ישירות את הנתונים שבידיה. למעשה אף אחד במכללת קינג לא ידע

שהנתונים בידינו.

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["I am ]inherently gloomy about the prospect of Africa [because] all our social policies are based on the fact that their intelligence is the same as ours—whereas all the testing says not really.” (October 2007)

["the ]historic curse of the Irish, which is not alcohol, it's not stupidity .But it's ignorance.” (2013)

“Stupidity is a disease and the "really stupid" bottom 10% of people should be cured”

“beauty could be genetically engineered, "People say it would be terrible if we made all girls pretty. I think it would be great.” (2003)

extracts of melanin – which gives skin its color – had been found to boost subjects 'sex drive. "That's why you have Latin lovers," he said, according to people who

attended the lecture. "You've never heard of an English lover. Only an English Patient".

1. Genes-the hereditary “factors” described by Mendel-were known to be associated with specific character traits, but their physical nature was not understood.Similarly, mutations were known to alter gene function, but precisely what a mutation isalso was not understood.

2 .The one-gene-one protein theory postulated that genes control the structure of proteins

3. Genes were known to be carried on chromosomes.

4 .The chromosomes were found to consist of DNA and protein

What was known about genes and DNA before Watson and Crick solved the structure of DNA?

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DNA is the genetic material: Frederick Griffith – Discovery of bacterial transformation

The bacteriumStreptococcus pneumonia

Smooth appearance

Rough appearance

1879-1941

Somehow, the cells debris of the boiled S cells

had converted the live R cells into live S cells(transformation)

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DNA is the genetic material of which genes and chromosomes are made

Oswald Avery1877-1955

“The most deserving scientist to not receive the Nobel Prize for his work”(though he was nominated for the award throughout the 1930s, '40s and '50s.)](2[

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The demonstration that DNA is the transforming principle

was the first demonstration that genes (the hereditary material)

are composed of DNA

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DNA is the genetic material: Avery et al. - transformation

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DNA is the genetic material: Hershey & Chase - transduction

Alfred Day Hershey (1908-1997) Nobel Prize winning in Physiology or Medicine in 1969, shared with Salvador Luria and Max Delbrück for their discovery on the replication of viruses and their genetic structure.

Martha Cowles Chase (1927-2003)

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Genetic map

Physical map (open reading frames – gene sequences)

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NOT like above, where the DNA must recombine and replace the endogenous copy, BUT where the DNA is extrachromosomal and persists as an episome (plasmid, F’, etc.)

In vitro

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NOT like above, where the DNA must recombine and replace the endogenous copy, BUT where the DNA is extrachromosomal and persists as an episome (plasmid, F’, etc.)

Lyse bacteria, collect the multipleCopies of plasmid DNA

- Sequence the DNA of the inserted gene B

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Genetic map

Physical map (open reading frames – gene sequences)

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