Dna recombination mechanisms
Download
1 / 40

DNA Recombination Mechanisms - PowerPoint PPT Presentation


  • 119 Views
  • Uploaded on

DNA Recombination Mechanisms. AHMP 5405. Objectives. List the major classes of mobile genetic elements (we went over this before) Describe the process of general recombination Diagram the process of gene conversion via Holliday junctions

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' DNA Recombination Mechanisms' - jackson-david


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

Objectives
Objectives

  • List the major classes of mobile genetic elements (we went over this before)

  • Describe the process of general recombination

  • Diagram the process of gene conversion via Holliday junctions

  • Describe ways by which site-specific recombination can influence DNA rearrangement and genetic regulation


Recombination repair

  • Present in prokaryotic and eukaryotic cells

  • Only poorly understood

  • We know it exists because UvrA- and RecA- cells are much more sensitive to UV than cells containing only one mutation


Why do chromosomes undergo recombination?

  • Deleterious mutations would accumulate in each chromosome

  • Recombination generates genetic diversity


Recombination

ABCDEFGHIJKLMNOPQRSTUVWXYZ

abcdefghijklmnopqrstuvwxyz

ABCDEFGhijklmnoPQRSTUVWXYZ

abcdefgHIJKLMNOpqrstuvwxyz


Mitotic and meiotic recombination

  • Recombination can occur both during mitosis and meiosis

  • Only meiotic recombination serves the important role of reassorting genes

  • Mitotic recombination may be important for repair of mutations in one of a pair of sister chromatids


Recombination mechanisms

  • Best studied in yeast, bacteria and phage

  • Recombination is mediated by the breakage and joining of DNA strands


The Holliday model

  • Two homologous duplexes are aligned

  • Strand exchange leads to an intermediate with crossed strands

  • This branch can move: Branch migration

  • The branch is resolved by cleavage and sealing










Action of depends on Ruv proteinsE. coli proteins in branch migration and resolution of Holliday structures


Chi structures depends on Ruv proteins

  • When plasmids recombine figure eight structure is formed

  • If the recombined plasmids are cut with a restriction enzyme a c (chi) is formed


Generation of a chi intermediate depends on Ruv proteins


Electron micrograph of the chi form depends on Ruv proteins


What does the Chi structure prove? depends on Ruv proteins

  • The fact that each pair of arms is the same length shows that the circles are joined at homologous sites


Recombination between homologous DNA sites depends on Ruv proteins

  • Recombination provides a means by which a genome can change to generate new combinations of genes

  • Homologous recombination allows for the exchange of blocks of genes between homologous chromosomes and thereby is a mechanism for generating genetic diversity

  • Recombination occurs randomly between two homologous sequences and the frequency of recombination between two sites is proportional to the distance between the sites



The mechanism of Cre- recombinationloxP site-specific recombination


Site specific recombination recombination

  • Viruses and transposable elements often integrate their genomes into the host chromosome

  • Site specific recombination is used by both eukaryotes and prokaryotes to regulate gene expression and to increase the organisms genetic repertoire



Mechanism recombinationof gene rearrangement


V(D)J recombination recombination



DNA non-homologous end-joining (NHEJ) recombination

  • Predominant mechanism for DSB repair in mammals.

  • Also exists in single-celled eukaryotes, e.g. Saccharomyces cerevisiae

  • Particularly important in G0/G1


DNA-PKcs recombination

Homologous recombination

Non-homologous end-joining

DSB

DSB

Rad50, Mre11, Xrs2 complex

Resection

Ku70, Ku80

Rad52

Rad50, Mre11, Xrs2 complex

Strand invasion

“Cleaning up” of ends

Rad51; BRCA2

DNA synthesis

XRCC4/Ligase IV

Ligation

Ligation, branch migration, Holliday junction resolution


DNA-PK recombination

DNA-PK

DNA-dependent protein kinase (DNA-PK)

DNA

ACTIVE

KINASE

INACTIVE


K recombination

u

7

0

K

u

8

0

DNA-PK has three subunits

D

N

A

X

P

D

N

A

-

P

K

c

s

K

u

7

0

K

u

8

0

6

9

k

D

a

D

N

A

-

P

K

c

s

8

3

k

D

a

A

T

P

A

D

P

4

7

0

k

D

a

A

C

T

I

V

E

I

N

A

C

T

I

V

E

Target sites: Ser/Thr-Gln


K recombination

u

7

0

K

u

8

0

DNA-PK has three subunits

D

N

A

X

P

D

N

A

-

P

K

c

s

K

u

7

0

K

u

8

0

6

9

k

D

a

D

N

A

-

P

K

c

s

8

3

k

D

a

A

T

P

A

D

P

4

7

0

k

D

a

A

C

T

I

V

E

I

N

A

C

T

I

V

E

… and is activated by DNA DSBs!




NHEJ: links to cancer recombination

  • Status of NHEJ helps to define clinical radiosensitivity:

    • Defects in DNA ligase IV associated with cells of a radiosensitive leukaemia patient (180-BR).

    • Levels DNA-PK correlate with clinical outcome (cervical cancer).

  • Inherited or somatic defects in DNA-PK system may lead to cancer.


ATM: deficient in ataxia-telangiectasia (A-T) recombination

  • Human autosomal recessive disorder

  • Progressive neurodegeneration

  • Cancer predisposition

  • Aspects of premature ageing

  • Radiosensitivity

  • Impairment in triggering cell cycle checkpoints in response to DNA DSBs


Rad24 recombination

Mec3

Ddc1

Rad9

Rad17

P

P

Tel1

Mec1

P

P

Chk1

Rad53

FHA

FHA

P

Dun1

FHA

Cdc25

DNA-damage signalling is conserved from yeast to man

S. cerevisiae

H. sapiens

S. pombe

P

Rad17

Rad17

Hus1

Hus1

Rad9

Rad9

Crb2

Brca1?

Rad1

Rad1

P

P

P

P

?

Lcd1

Rad26

Tel1

ATM

ATR

Rad3

P

p53

P

P

P

P

P

Chk1

Chk1

Cds1

Chk2

FHA

FHA

Cdc25C

Cdc2 activation

Pds1 destruction

Cdc5

Cdc2 (Cdk1)

G1-S

Esp1 activation

Crt1, Sml1?

activation


ad