Lecture 8

Question 1

Describe T7

Answer 1

Podoviriae

Naked icosahedral capsid

60 nm
Short tail and tail fibres
Lytic, no lysogeny
Linear dsDNA genome, 40kbp
- 56 genes
- 59 proteins
- 150bp terminal repeats (two terminal repeats important for replication)
Phage receptor: Lipopolysaccharide

Question 2

T7 genome: multiple promoters, terminate at the ____ site

Answer 2

Same

Question 3

What are the three classes of T7 genome?

Answer 3

Class I: early
Class II: DNA metabolism
Class III: Virion structure and assembly

Question 4

What are the Class I proteins of T7?

Answer 4

Gene 0.3: Inhibits host type 1 restriction endonucleases so that genome is not cleaved

Gene 0.7: inhibits E. coli RNA pol.
Gene 1: T7 RNA pol.

Question 5

What transcribes the Class 1 proteins of T7?

Answer 5

E. Coli RNA pol

Question 6

What transcribes the class II proteins in T7?

Answer 6

T7 RNA pol.

Question 7

What kind of class II proteins are created in T7?

Answer 7

1.3: DNA ligase, join lagging-strand DNA
2: Inhibit E. coli RNA pol
3. Endonuclease, degrades host DNA, cleaves T7 DNA concatermer
3.5: Lysozyme, inhibits T7 RNA pol
4: RNA primase/helicase
5: DNA pol
6. Exonuclease, degrades host DNA

Question 8

What transcribes the Class III T7 proteins?

Answer 8

T7 RNA pol

Question 9

What are the Class III proteins in T7?

Answer 9

8: Portal protein
9: Scaffolding protein
10: Capsid protein
11: Tail protein

Question 10

What problem does concatemers solve in T7?

Answer 10

DNA polymerase needs a primer to initiate DNA synthesis
RNA primer at the 3’ end of template DNA cannot be removed or replaced with DNA
Result in loss of sequence

Question 11

How are concatemers formed?

Answer 11

Lecture 8 slide 12

Question 12

Describe T7 DNA replication

Answer 12

Bidirectional
Resembles E. coli DNA synthesis: leading and lagging strand
T7 encodes all its own DNA replication proteins
Unique origin 5.9kb from left of genome
- Prevents RNA polymerase and DNA replication fork collisions
DNA replication is initiated by T7 RNA polymerase
Large concatemers of T7 genomes are formed via 150bp terminal repeats

Question 13

Describe the Lambda bacteriophage

Answer 13

Siphoviridae
DsDNA: 40-60kbp, ssDNA extension (Cohesive ends)
Temperate bacteriophage: Lysogenic phase
Icosahedral head: 63nm diameter
Tube like tail: 135 nm long, non-contractile
Receptor: Sugar transport proteins LamB (maltose transporter)

Question 14

What are temperate phases?

Answer 14

Able to grow lyrically or exist as a repressed prophage

Question 15

What is a prophage?

Answer 15

Integrated phage DNA, lytic genes are repressed, passively replicate with host chromosome

Question 16

What is a lysogen?

Answer 16

Bacteria carrying prophage

Question 17

True or false: lambda is both lytic and lysogenic

Answer 17

True

Question 18

How is transcription regulated in the lambda phage?

Answer 18

Transcription initiation: has activator and repress or
Transcription termination: has antiterminator