Viral Gene Regulation

Question 1

viral regulation

Answer 1

• occurs during transcription initiation for host and viral genes
• viruses do not have the cellular machinery to regulate and express their own genes
• expression of viral genes is closely tied to reproduction inside the host cell

Question 2

lysogenic cycle

Answer 2

• virus incorporated its genetic material into that of the host cell
• viral genome replicated along with the host cell
• creates a prophage/provirus
• viral genes NOT expressed

Question 3

lytic cycle

Answer 3

• host cell used to produce a new generation of virions
• cell is lysed and virus moves onto a new cell
• phage co-opts the bacterial cell’s expression machinery to express their own viral genes

Question 4

viral promoters

Answer 4

• positive regulation of transcription initiation
• virus evolved to create promoters that are similar to that of the host genes
• bacterial RNA polymerase and sigma factors recognize this promoters of early viral genes
• natural selection

Question 5

primary event after a phage injects its genome

Answer 5

host bacterium’s RNA polymerase begins to transcribe early viral genes

Question 6

viral early gene products

Answer 6

• regulatory proteins
  1. act to deactivate bacterial sigma factors, shutting down expression of host genes (-)
  2. act to increase product of genes associated with DNA synthesis machinery (+)
  3. act as activators for the transcription of late genes, helping RNA polymerase transcribe them

Question 7

viral late genes

Answer 7

• encode structural proteins and enzymes
  1. capsid
  2. phage protein
  3. lysis enzyme

Question 8

How does the virus make sure that early and late viral genes are expressed at the same time?

Answer 8

the genes are organized into operons

Question 9

lysis enzyme

Answer 9

dissolves the host cell so that the newly created phages can infect other cells

Question 10

HIV

Answer 10

• retrovirus that reverse-transcribes its RNA into the host’s DNA so that it can express the viral DNA
• RNA polymerase transcribes host genes

Question 11

transcription elongation

Answer 11

• usually prevented by the host cell
• identifies the growing RNA strand as undesirable and discontinues transcription
• negative regulation
• used by all eukaryotes, not just infected ones

Question 12

TAT

Answer 12

• prevents the host cell from regulating viral genes at transcription elongation
• binds to the 5’ end of elongating mRNA and helps it complete transcription
• positive regulation