The previous exercise dealt with differentiation, and specifically with the events
leading to differential gene activity. In olecular terms, this process involves
regulation using DNA as a primer molecule for the selective synthesis of RNA.
DNA-primed RNA synthesis is termed “transcription.”
Transcription is a complex series of reactions which involve the use of an
RNA polymerase enzyme, known as transcriptase. If the reaction occurs in
reverse, that is, with an RNA primer synthesizing DNA, the process is known
as reverse transcription, and the enzyme is reverse transcriptase. This latter
process is important for RNA virus replication in general, and is most significant
when examining oncornagenic virus. Oncornagenic viruses are RNA-containing
viruses that are also causal agents for some forms of cancer (primarily in birds).
Reverse transcription is also important in the development of amphibians, and in the process of gene amplification.