Tobacco Mosaic Virus (TMV) Structure and Replication

In this article we will discuss about the structure and replication of Tobacco Mosaic Virus (TMV).

Table of Contents

TMV Structure

Tobacco Mosaic Virus (TMV) is a straightforward rod-shaped helical virus, and it is made up of a single strand of RNA (5.6 percent) that is positioned in the centre and is surrounded by a protein sheath (94.4 percent). The diameter of the rod is around 180 microns, and its length is estimated to be 3,000 microns.

The protein shell is referred to by its technical name, capsid. R. Franklin calculated that there are 2,130 sub-units, also known as capsomeres, in a complete helical rod, and that there are 49 capsomeres on every three turns of the helix (Figure 1). As a result, there are approximately 130 turns in each rod of TMV.

Tobacco Mosaic Virus

Figure 1: Tobacco Mosaic Virus (TMV) Structure

The RNA molecule is located approximately 50 Å inward from the rod’s outermost surface. The RNA helix has a diameter of approximately 80Å. The diameter of the rod’s central core is approximately forty degrees. According to Knight’s research, each capsomere has the shape of a grape and is composed of approximately 158 amino acids. Its molecular weight is 17,000 daltons.

The length of the ssRNA is only little greater than 3300 Å, and it is slightly projecting from one end of the rod. About 7300 nucleotides make up the RNA molecule, which has a molecular weight of about 25,000 daltons and contains these nucleotides in a linear arrangement.

TMV Replication

Plant viruses such as TMV are able to infiltrate and enter all of the host cells; their replication process then takes place entirely within these infected host cells. The viral nucleic acid is released into the cytoplasm of the host cell once the protein covering on the virus breaks apart inside the host cell (Figure 2).

Even if the locations of the various stages of viral multiplication and the production of new viruses have not yet been determined with complete confidence, the research suggest that after viral-RNA becomes free in the cytoplasm of the cell, it goes into the nucleus of the cell (possibly into the nucleolus).

First, the viral RNA is responsible for inducing the production of certain enzymes that are referred to as ‘RNA polymerases.’ Next, the single-stranded viral RNA is responsible for producing an additional RNA strand that is known as replicative RNA.

Figure 2: Tobacco Mosaic Virus (TMV) Replication

This strand of RNA is complementary to the genome of the virus and acts as a “template” for the production of new RNA single strands, which are copies of the viral-RNA that was present in the parent virus. The newly created viral RNAs are exported from the nucleus into the cytoplasm, where they take on the function of messenger RNA (mRNAs). The production of protein subunits is guided by each individual mRNA, which works in concert with the ribosomes and t-RNA of the host cell.

After the desired protein subunits, known as capsomeres, have been generated, the new viral nucleic acid is thought to assemble the protein subunit around it, culminating in the development of the full virus particle, known as the virion.

There is no ‘lysis’ of the host cell, which is what happens when virulent bacteriophages infect a cell. The infecting viruses don’t kill the host cells, so they can spread throughout the body and cause a systemic infection. Other healthy plants can become infected with the virus if it is communicated in some way.