PRESENTATION ON T7 BACTERIOPHAGE.pptx

This ppt is about the T7 phage, it's structure, reproduction, and its genome.

1. PRESENTATION ON T7 BACTERIOPHAGE JANANI K R III B.Sc., MICROBIOLOGY

2. INTRODUCTION A virus which infects the bacteria called bacteriophage . T7 bacteriophage infects most strains of Escherichia coli . T7 bacteriophage is a T-odd phage. Bacteriophage T7 has a lytic life cycle meaning that it destroys the cell it infects. Bacteriophage T7 is also known as Entereobacteria phage . In 1945 study by Demerec and Fano , T7 was used to describe one of the seven phage types (T1 to T7) that grow lytically on E.coli . The genetic material of T7 bacteriophage is dsDNA .

3. STRUCTURE OF T7 BACTERIOPHAGE T7 bacteriophage is composed of icosahedral head , a connector and flexible tail . The icosahedral head has a diameter of 60 to 61nm with a capsid that is 2nm thick. The capsid is composed of two forms of the gene 10 protein. The head-tail connector is composed of 12 gp8 molecules. The connector has a 12-lobed wide domain inserted into the head cavity and a narrower domain that interacts with the tail. Inside the head, and attached to the connector in the coaxial orientation, is a 26nmx21nm cylindrical structure that is usually referred to as the internal core.

4. The core has recently been shown to exhibit 8-fold symmetry, it consists of stacked rings and contains three distinct proteins, the products of genes 14,15,and 16. The tail is 23nm long, tapering from a diameter of 21nm at the connector to 9nm at its distal end, and is known to consist of two major proteins gp11 and gp12. Attached near the head proximal end of the tail are six symmetrically positioned tail fibers. Each fiber is composed of a trimer of gp16 that forms a kinked structure.

5. GENOME OF T7 BACTERIOPHAGE The genome of phage T7 was among the first completely sequenced genomes and was published in 1983 . The head of the phage particle contains the roughly 40kbp dsDNA genome which encodes 55 proteins . The genome features numerous overlapping genes that were partially removed through ‘ refactoring ’ the genome to produce.

6. REPRODUCTION OF T7 BACTERIOPHAGE The T-phages, T1 through T7, are referred to as lytic phages because they always bring about the lysis and death of their host cell, the bacterium E.coli . Lytic cycle is known as reproductive cycle of bacteriophage. Lytic cycle is also called as Master-Slave action . In the life cycle of phage T7 virus acts as master and host as slave. T7 bacteriophage that only use the lytic cycle s o it is called as virulent phage . T7 bacteriophage has a life cycle of 17 min at 37 degree celsius . Lytic cycle has five steps which are adsorption, penetration, synthesis, maturation and release.

7. Step 1: Adsorption Attachment sites on the bacteriophage adsorb to receptor sites on the host bacterium, E.coli . T7 bacteriophage adsorb to the bacterial cell wall by its tail fibers. This is the first step in lytic cycle known as adsorption and also known as attachment . Step 2: Penetration Following adsorption, the phage secrete certain enzyme, to “drills” a hole in the bacterial cell wall . Then the bacteriophage injects its genome into the bacterial cytoplasm. This process is called penetration .

8. Step 3: Synthesis Immediately after the injection of the viral DNA there is a process initiated called synthesis . Synthesis of Early Proteins Synthesis of early proteins refers to the transcription and translation of a section of phage DNA to make a set of proteins that are needed to replicate the phage DNA. The early proteins produced a repair enzyme to repair the hole in the bacterial cell wall. A DNAase enzyme that degrades the host DNA into precursors of phage DNA and a virus specific DNA polymerase that will copy and replicate phage DNA.

9. The result is the synthesis of several copies of the phage DNA. Synthesis of late proteins After the synthesis of early proteins, the next is the synthesis of late proteins. Each of the several replicated copies of the phage DNA can now be used for transcription and translation of a second set of proteins called the late proteins. The late proteins are mainly structural proteins that make up the capsomeres and the various components of the tail assembly. Lysozyme is also a late protein that will be packaged in the tail of the phage.

10. Lysozyme used to escape from the host cell during the last step of the replication process. Step 4: Maturation Following synthesis of proteins, maturation takes place. The proteins that make up the capsomeres assemble themselves into the heads and “ reel in ” a copy of the phage DNA. The tail and accessory structures assemble and incorporate a bit of lysozyme in the tail fibers. The phage arrange their escape from the host cell during the assembly process.

11. Step 5: Release After the assembly of new phages, the phage secretes the lysozyme enzyme that lysis the cell wall of host bacterium, E.coli and the matured new phages release and reinfects the strains of E.coli . Step 6: Reinfection After the release of the new phages, T7 phage is ready to reinfect the another strain of E.coli.

12. REPRODUCTION OF T7 BACTERIOPHAGE

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