Basic Transcription Part 3

Question 1

Lytic Phase

Answer 1

• infection
• phage DNA cyclizes
• decision point
• phage DNA replicates (rolling circle)
• phage heads, tails, and DNA assemble into progeny phages
• cell lysis
• reinfection

Question 2

Lysogenic Phase

Answer 2

• infection
• phage DNA cyclizes
• decision point
• integration of phage DNA
• cell division
• phage DNA replicates
• goes through lytic cycle

Question 3

Lysogenic mode

Answer 3

• early genes transcribed and translated by host
• lambda repressor binds 2 phage operons
• shuts down all other transcription (genes needed for lysis)
• phage integrates into host genome

Question 4

lysogen

Answer 4

• a bacterium contining integrated phage DNA

Question 5

prophage

Answer 5

• integrated phage DNA

Question 6

when lysogen encounters mutagenic chemicals

Answer 6

• phage can enter lytic cycle

Question 7

DNA

Answer 7

• linear in phage and circular soon after infection

- brings together all late genes that are separated when the phage is linear

Question 8

3 phases of transcription

Answer 8

1. immediate early
2. delayed early
3. late

• 3 class arranged sequentially on phage DNA

Question 9

program of gene expression controlled by

Answer 9

• antitermination

- transcriptional switches

Question 10

immediate early genes

Answer 10

• PL - N

- PR- cro

Question 11

PL

Answer 11

• promoter to the left

Question 12

N

Answer 12

• antiterminator

Question 13

PR

Answer 13

• promoter to the right

Question 14

cro

Answer 14

• repressor of lambda repressor

Question 15

Delayed early genes for lysis

Answer 15

• Q antiterminator

Question 16

Q antiterminator

Answer 16

• permits transcription of late genes

Question 17

Delayed early genes for lysogeny

Answer 17

• CII and CIII lead to CI expression

Question 18

late genes

Answer 18

• only transcribed when cell will undergo lysis

- not when phage integrates

Question 19

immediate early genes

Answer 19

• host RNA polymerase binds PR and PL

- transcribes immediate early genes first

Question 20

two immediate early genes

Answer 20

• cro
• N
• transcribed from PR and PL

Question 21

polymerase encounters what when transcribing immediate early genes

Answer 21

• rho-dependent terminators

- encounters before delayed early genes

Question 22

delayed early genes

Answer 22

• cro repressor blocks transcription of lambda repressor genes

Question 23

lambda repressor gene

Answer 23

• CI

- located between two promoters

Question 24

N antiterminator

Answer 24

• causes RNA polymerase to ignore terminators and transcribe delayed early genes

Question 25

same promoters are used for

Answer 25

- immediately and delayed early gene expression

Question 26

delayed early genes are important to

Answer 26

- continue lytic cycle | - establish lysogeny

Question 27

Genes O and P for lysis

Answer 27

- Genes O and P code for proteins needed for phage DNA replication

Question 28

late genes

Answer 28

- all transcribe in rightward direction - not from PR - proteins that make up phage head and tail - proteins that lyse host cell

Question 29

late promoter

Answer 29

- PR' | - located just downstream of Q

Question 30

in absence of Q

Answer 30

- transcription of from PR' terminates after 194 bases

Question 31

N+Q

Answer 31

- anti terminators | - work via a different mechanism

Question 32

Two delayed early genes help establish lysogeny

Answer 32

- some needed for integration of phage DNA into host genome - prerequisite for lysogen - products of cII and cIII genes allow transcription of cI gene = lambda repressor

Question 33

lambda repressor

Answer 33

- central component in lysogeny | - repressor of lysis

Question 34

anti termination by N

Answer 34

- N is immediate early gene

Question 35

in absence of N

Answer 35

- transcription from PL produces N and termination occurs downstream

Question 36

N protein binds

Answer 36

- the N transcript at the N utilization site - binds to its own transcript - allows polymerase to go through rho-dependent terminator and continue on and allow readthrough

Question 37

nut site

Answer 37

- contains an inverted repeat - probably forms a stem loop - RNA must loop out

Question 38

processive

Answer 38

- anti termination factors remain associates with polymerase as it moves down DNA - not terminated

Question 39

lambda phage

Answer 39

- virus that infects E. coli cell