Bacteriophage λ and P1 are both temperate phages. Which one of the following statements made about these phages and their lytic and lysogenic cycles in E. coli is INCORRECT?

Correct option is C

Explanation:

• Bacteriophage λ and P1 are both temperate phages, meaning they can undergo either lytic or lysogenic cycles in E. coli. However, their lysogenic states differ significantly.

1. Statement 1: Correct 

   • Both λ (lambda) phage and P1 phage are double-stranded DNA (dsDNA) viruses, meaning they have a dsDNA genome.
   • This characteristic is common among many temperate phages.

2. Statement 2: Correct 

   • In their lysogenic state:
     • λ phage integrates into the E. coli genome as a prophage.
     • P1 phage, however, does not integrate into the genome. Instead, it remains as a low-copy-number plasmid, autonomously replicating within the host cell.
   • This statement correctly distinguishes between the behaviors of λ and P1 phages.

3. Statement 3: Incorrect 

   • The λ phage integrates into the bacterial chromosome as a prophage in lysogeny.
   • P1 phage does not integrate into the genome but persists as a plasmid.
   • Since this statement incorrectly states that both phages integrate, it is incorrect.

4. Statement 4: Correct 

   • In their lytic cycle, both λ and P1 phages replicate their DNA as plasmids before packaging new virions.
   • P1 is always found in a plasmid form, and λ may transiently form plasmid-like intermediates before the lytic cycle progresses.

Information Booster:

1. Lambda (λ) phage integrates into the E. coli genome at the attB site using the integrase enzyme.
2. P1 phage does not integrate but replicates as a low-copy-number plasmid.
3. Lytic cycle: Both phages produce virions that cause cell lysis to release new viruses.
4. Lysogenic cycle: λ phage integrates into the host genome, while P1 phage remains extrachromosomal.
5. P1 phage uses a partitioning system to ensure stable inheritance of its plasmid form.
6. Both phages have site-specific recombination systems, but only λ undergoes true integration into the chromosome.
7. The Cre-loxP recombination system used in molecular biology is derived from the P1 phage.