Textbook Chapter 8 Bacteriophage Lambda

Question 1

what is a bacteriophage lambda?

Answer 1

a temperate phage that can integrate its DNA into the host cell chromosome and repress all phage gene expression, creating a lambda lysogen

Question 2

induction of lytic gene expression in a lysogen involves what?

Answer 2

inactivation of the lambda CI repressor by self cleavage stimulated by cellular RecA protein

Question 3

in the absence of sufficient concentrations of CI repressor, transcription begins where?

Answer 3

at promoters PL and PR on the lambda chromosome, but terminates shortly downstream at terminators tL1 and tR1

Question 4

early gene products include proteins that do what>

Answer 4

excise and circularize lambda DNA, DNA replication proteins, and another antiterminator protein, Q

Question 5

the Q protein allows transcription to do what?

Answer 5

proceed rightward on circular lambda DNA, transcribing all “late” genes in a single, long transcript

Question 6

the level of the CI repressor is determined in part by what?

Answer 6

the concentration of CI, which activates synthesis of its own transcript when at low concentrations, but represses its synthesis when at high concentrations

Question 7

the Cro repressor is made from what?

Answer 7

initial transcript starting at PR

Question 8

what does the Cro repressor do?

Answer 8

suppresses synthesis of the CI transcript when at high concentrations allowing lytic growth

Question 9

what determines whether an infected cell will become a lysogen or enter the lytic cycle?

Answer 9

a complex set of interactions among repressors and operators as well as the phage CII and CIII proteins

Question 10

rolling circle replication makes what?

Answer 10

long concatemers of lambda DNA that are cleaved and packaged into proheads. Scaffolding proteins are shed during packaging