What are Lambda Phage Discovery Features?

Discovery Process and Features of Lambda Phage

Meaning of Lambda phage: Lambda phage is a mild phage that injects genomic DNA into E. coli through a tail tube, leaving its protein coat outside the bacteria. 

After entering the human bacteria, the DNA is double-stranded with 12bp complementary single-stranded sticky ends at both ends, which can proliferate in two different ways.

In 1951, J. Lederberg's wife, Esther Lederberg, proved that the K12 used by J. Lederberg and Tatum to hybridize had a prophage and named it "λ". After 10 years of research, the essence of its lysogenization was found out.

Name:    Lambda phage

Discoverer:    Esther Lederberg

Field:    Biology / Virology

Definition:    A mild phage

Discovery time:    1956

What is the Discovery process of Lambda phage?

Lambdaphage Discovery Process: E. coli K12 is the presence of prophage. Jacob and Wollman (1956) discovered the phenomenon of zygotic induction and used zygotic induction to determine the integration sites of several prophages on the E. coli chromosome.

They found that the frequency of the recombiners obtained by Hfr (λ) × F- is much lower than that of Hfr × F- (λ) or Hfr (λ) × F- (λ).

This is because in the Hfr (λ) × F- hybridization, the prophage enters the cytoplasm of the recipient without repressor.

A large number of copies are made to lyse the recipient cell, so it is not easy to obtain recombinants. This phenomenon is called zygote induction. 

Let's go back and look at the transfer level mapping, interrupted hybridization experiments and recombination mapping are using Hfr × F- (λ) because it does not cause zygote induction.

What are the Features of Lambda Phage?

Lambda phage is a mild phage of the long-tailed phage family. Lambda phage is a double-stranded DNA phage with an icosahedron head with a diameter of 55nm and a non-contracting tail with a slender tail wire at the end.

DNA is a linear molecule with sticky ends, that is, a single-stranded extension of 12 nucleotides, so the linear genome can be immediately circularized after infection. 

Lambda DNA has a phage binding site that can form a base pair with a bacterial binding site. 

The bacterial binding site is located between the galactose or gal operon and the biotin operon on the E. coli chromosome.

Prophage

After the two sites are paired, the integrase catalyzes the viral and bacterial DNA strands and physical exchange with the help of a specific host protein. 

The circular lambda DNA is linearly integrated into the E. coli DNA adjacent to the gal operon, which is called Prophage. 

The lambda phage has a genome of 50 Kb and 61 genes, of which 38 are more important. Its life history is shown in Figure which can be divided into lysis cycle and lysogen cycle.

When the bacterium is in a lysogenic state, there are some products of the λ CI gene in the cytoplasm, CI protein.

This is a repressor protein that can prevent the transcription of the two early promoters of λ and λ, making it can not produce some replication and cell lysis proteins. 

Lambda DNA replication

Lambda's DNA replicates as the host's chromosome replicates. However, under UV induction, Rec protein can degrade CI protein (see Chapter 17), and induce 90% of cell lysis. 

Sometimes λ can also spontaneously (10-5) free from the host's chromosome and replicate, eventually leading to the lysis of the host cell. This is called curing. 

The lambda free in the cytoplasm can be subjected to rolling circle replication, producing multiple copies, synthesizing head and tail proteins, packaging into a complete lambda phage, lysing the cells, releasing the lambda phage and infecting new cells.

Conclusion

Because the DNA of lambda phage is also integrated on the chromosome and free from the cytoplasm, it is also called episome. But unlike factor F, lambda phage has an extracellular form, while factor F has no extracellular form.

Author's Bio

Dr. Shawna Reason

Name: Shawna Reason

Education: MBBS, MD

Occupation: Medical Doctor / Virologist 

Specialization: Medical Science, Micro Biology / Virology, Natural Treatment

Experience: 15 Years as a Medical Practitioner

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