Question: a temperate bacteriophage has the Gene order: x1 x2 x3 att x4 x5. A.Wh

Question

Question: a temperate bacteriophage has the Gene order: x1 x2 x3 att x4 x5.

A.What is the gene order of the prophage?

B. Can the lytic p1 phage infect the lysogen produced by integration of the phage described in question part A?(hint. The phage in part A is Lambda)

C. Describe the sequence of events that occur when the virulent phage T4 infects susceptible host cells.

D. A new series of rII mutations in the virulent phage T4 has been isolated and the results of phage recombination experiments between all twelve of the new mutations are shown in picture. Draw a linear genetic map showing the location of all point mutations and the frequency of recombination between adjacent mutations and describe the location and extent of all deletions.

Explanation / Answer

A) att x 4 x 5 x (cos site) x 1 x 2 x 3 x att

B) No. In lysogen phage integration produces a repressor protein which inhibits with the late genes of phage required for lytic phase. This repressor protein immunizes the lysogen for lytic phages. A good example is bacteriophage lambda in which repressor protein competes with cro protein to shut off late phage genes required for lytic cycle.

C) Infection of virulent bacteriophage T4 into host cell involves following events:

1. Adsorption

This step is mediated by the tail fibers which binds to specific receptors on the bacterial cell such as proteins on the outer surface of the bacterium, LPS, pili, and lipoprotein. Initially the process is reversible but one or more components of base plate mediates irreversible binding of phage to a bacterium.

2. Penetration

The bacterial sheath contracts and the hollow tail fiber is pushed through the bacterial envelope. Nucleic acid from the head passes through the hollow tail and enters the bacterial cell. The structure of virus outside the bacterium remains as "ghost".

3. Biosynthesis of proteins

The phage nucleic acid takes over the host biosynthetic machinery and phage specified m-RNA's and proteins are made. virus T4 changes the sigma factor of the host by producing an anti-sigma factors so that the host promotors are not recognized any more. One of the first polypeptides to be translated destroys the host's DNA. During this phase phage T4 transcribes two types of genes : immediate early genes and delayed early genes

4. Maturation, lysis and release

The assembly of phage components into mature infective phage particle is known as maturation. In Lysis and Release Phase the bacteria begin to lyse due to the accumulation of the phage lysis protein and intracellular phage are released into the medium.

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