Читать книгу Principles of Virology - Jane Flint, S. Jane Flint - Страница 266

Historically, viral RNA-dependent RNA polymerases were given two different names depending on their activities during infection. The term replicase was used to describe the enzyme that copies the viral RNA to produce additional genomes, while the enzyme that synthesizes mRNA was called transcriptase. In some cases, this terminology indicates true differences in the enzymes that carry out synthesis of functionally different RNAs, but for other RNA viruses, genomic replication and mRNA synthesis are the same reaction (see the figure). For double-stranded RNA viruses, mRNA synthesis produces templates that can also be used for genomic replication. As these formerly applied terms can therefore be inaccurate and misleading, they are not used here. The name RNA-dependent RNA polymerase (RdRP) will be used in this textbook to describe the enzymes that carry out genome replication and mRNA synthesis from viral RNA templates.

The production of mRNAs from viral RNA templates is often designated transcription. However, this term refers to a specific process, the copying of genetic information carried in DNA into RNA. Consequently, it is not used herein to describe synthesis of the mRNAs of viruses with RNA genomes; this process will be called mRNA synthesis. Similarly, use of the term promoter is reserved to designate sequences controlling transcription of DNA templates.