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Genetic Information in Bacterial Cells

2

Bacterial Reproduction: Binary Fission

Bacterial chromosome and Plasmids to each

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Types of Gene Transfer in Bacterial Cells

Transformation - ‘naked’ DNA fragments from donor to recipient

Transduction - Virus carries DNA fragment from donor to recipient

Conjugation - Cell : Cell contact required

Donor cell: F +, Hfr

Recipient: F -

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Gene Transfer in Bacteria

Linear or circular DNA is transferred

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Transformation

DNA from

disrupted donor

Homologous

Recombination

Double CO

Heteroduplex

DNA replication

Closely linked genescointegrate

Transformantwith new phenotype

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Transformation: Determining Gene Order

Would you see

p+ q o+

transformants?

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Transformation: Determining Gene Order

Sample problem

Least frequent, so a-b far aparta-c closer togetherb-c closer together

Therefore a - c - b

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Transduction: Life Cycle of Phage

Lytic

or

Lysogenic

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Transduction: Generalized

Fragments of bacterial

chromosome randomly

packaged into phage

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Transduction: Generalized

Integration requiresDCO

Cotransductionindicates linkage

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Transduction: Specialized

Phage

integrates

Takes

specific gene

with it during

excision

12

Conjugation

Lederberg & Tatum (1946) Davis (1946)

Cell contact required

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Conjugation

Sex pilus (F-pilus) F+ cells

F factor - plasmid

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Conjugation: F+ x F- mating

F factor nicked at origin

Rolling circle replication

Linear transfer of genes

5 4 3 2 1 F

Recipient becomes F+

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Conjugation: Origin of Hfr cells

F factor integrates

a

b

cm

p

p m c b a

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Conjugation: Hfr x F- cells

New genes must integrate into bacterial chromosome

Trans-conjugant

still F-

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Conjugation: Transfer of Genes from Hfr Cell

Genes transferred in order

Minute mapping possible

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Conjugation: Transfer of Genes from Hfr Cell

Minute Mapping

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Conjugation: Interrupted-Mating with Hfr Strains

Determine gene order,position and orientation of F factors

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Conjugation: Sample Problem Hfr Mapping

Indicate positon of

each gene,

each F-factor,

and orientation

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Conjugation: Determining Gene Order

Also applicable to Transformation and Transduction

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Conjugation: Determining Gene Order

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Conjugation: Determining Gene Order

Order is d-f-e or e-f-d

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Conjugation: Origin of F’ Strains

F’ cell

Transfers specific genes

Recipient - merozygote

partial diploid

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Genetic Analysis of Viruses

Viruses - small genome, rapid reproduction

large numbers enable mapping within genes

(1 in 1012 recombinants observed)

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Benzer’s Experiments: T4 bacteriophage

Wild type Rapid lysis (rII) mutants

Small rough plaques Large round plaques

Grow in E. coli Grow in E. coli

Strains B and K12 Strain B , NOT K12

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Benzer’s Experiments: T4 bacteriophage

Complementation tests with numerous rII mutants

K12 K12

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Benzer’s Experiments: T4 bacteriophage

Intragenic mapping of independently isolated rII A mutants

Transfer to strain K12 to select for wild-type recombinantsFrequency = distance between different mutation

E.coli B

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Deletion Mapping

Facilitates mapping of mutations

If mutation is in region of deletion, no wild-type recombinants occur.

If mutation is in different region, wild-type recombinants will occur.

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Deletion Mapping: Sample Problem 1

Locations of

deletions (white)

and DNA ( )

Where is a3located?

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Deletion Mapping: Sample Problem 2

Line represents deletion, intact DNA is not shown

Where is a3located?

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Deletion Mapping: Complete map of rII locus

Locations of