Reverse Transcription Process

Reverse Transcription:

This phenomenon was studied by Temin and Baltimore in 1972 and is thus known as Teminism. While studying the activity of double-stranded RNA containing Rous Sarcoma Virus (RSV) in the cancerous tissue, they found that viral RNA synthesized DNA complementary to its strands. As soon as the RNA of RSV comes in contact with the cytoplasm of the host cell, it synthesizes the enzymes that are called reverse transcriptase. It catalyzes the conversion of RNA to DNA copy and exhibits a reverse phenomenon of the normal process. Such a phenomenon is known as the reverse transcription process. Once the DNA complementary to viral RNA is synthesized it follows the normal rule and synthesizes viral RNA and viral proteins as depicted in the following figure:

The central dogma says that the flow of information is unidirectional, DNA → RNA → protein. However, with the discovery of the enzyme reverse transcriptase, it becomes clear that RNA can also go back to DNA as represented here:

DNA ==== RNA → Protein

This is a characteristic of retroviruses and this is not followed by other RNA viruses. The virus HIV–III (Human immunodeficiency virus-III) which is responsible for causing AIDS disease is also a retrovirus. About twenty viral genes have been identified which are responsible for triggering cancer in cells. On the other hand, slightly modified versions of these genes are also present in normal cells which are known as protooncogenes or cellular oncogenes. Most of the cellular oncogenes code for growth factors or for proteins required for growth factor action such as receptors. The origin of cancer is a complex phenomenon, where viral oncogenes or activated cellular oncogenes products are responsible for the unconditional growth of cells.