Joshua Lederberg

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Discovery of transduction
Norton Zinder 1928 2012
Joshua Lederberg 1925 2008
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.
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Discovery of transduction
1. Started with phe-, trp-, tyr- and met-, his-,
from the bacterium Salmonella typhimurium 2.
After the two strains were mixed wild type
prototrophs appeared at 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
the agent responsible for gene transfer was the
same size as a known phage of salmonella called
phage P22
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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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Phage plaques
Micro -gt Macro? With plaques.
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I. Mapping phage chromosomes using phage crosses
h- can infect two different E.coli strains
(strains 1 and 2)
h can infect only strain 1
r- rapidly lyses cells, thereby producing large
plaques
r 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.
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I. Mapping phage chromosomes using phage crosses
h clearness (here- color) of plaque r
size of plaque
h-r
hr-
x
h-r
hr-
h-r-
hr
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 plaque 4. Phage plaques with the allele
(h) can infect only strain 1, forming a cloudy
plaque
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I. Mapping the genome of a virus
(h r) (h- r-) total plaques
RF
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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
P1 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 recombination NOT 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-duction
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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)
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Linear scale drawing of a 5-minutes section of
the 100-minute 1990 E.coli linkage map (1990,
total of more then 1400 genes)
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September 1997-The complete sequence of the E.
coli genome
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Correlation of the genetic and physical maps
Genetic map
Physical map (open reading frames gene
sequences)
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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. Watson 1928 (age 84)
Francis Crick 1916-2004
Maurice Wilkins 1916-2004
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".
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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.
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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 ourswhereas 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."
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What was known about genes and DNA before Watson
and Crick solved the structure of DNA?
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 is also 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
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DNA is the genetic material Frederick Griffith
Discovery of bacterial transformation
The bacterium Streptococcus pneumonia
Rough appearance
1879-1941
Smooth appearance
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
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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
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Genetic map
Physical map (open reading frames gene
sequences)
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In vitro
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.)
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Lyse bacteria, collect the multiple Copies of
plasmid DNA -Sequence the DNA
of the inserted gene B
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.)
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Genetic map
Physical map (open reading frames gene
sequences)