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A reverse transcriptase (RT) is an enzyme used to convert RNA genome to DNA, a process termed reverse transcription.Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genomes, by retrotransposon mobile genetic elements to proliferate within the host genome, and by eukaryotic cells to extend the telomeres at the ends of their linear chromosomes.
Viral replication is the formation of biological viruses during the infection process in the target host cells. Viruses must first get into the cell before viral replication can occur. Through the generation of abundant copies of its genome and packaging these copies, the virus continues infecting new hosts. Replication between viruses is ...
RdRps are highly conserved in viruses and are related to telomerase, though the reason for this was an ongoing question as of 2009. [4] The similarity led to speculation that viral RdRps are ancestral to human telomerase. [5] The most famous example of RdRp is in the polio virus.
Some −ssRNA viruses are ambisense, meaning that both the negative genomic strand and positive antigenome separately encode different proteins. In order to transcribe ambisense viruses, two rounds of transcription are performed: first, mRNA is produced directly from the genome; second, mRNA is created from the antigenome.
Positive-strand RNA virus genomes usually contain relatively few genes, usually between three and ten, including an RNA-dependent RNA polymerase. [4] Coronaviruses have the largest known RNA genomes, between 27 and 32 kilobases in length, and likely possess replication proofreading mechanisms in the form of an exoribonuclease within nonstructural protein nsp14.
Transcription of mRNAs initiated by viral polymerase using cap snatching. The first step of transcription for some negative, single-stranded RNA viruses is cap snatching, in which the first 10 to 20 residues of a host cell RNA are removed (snatched) and used as the 5′ cap and primer to initiate the synthesis of the nascent viral mRNA. [1]
The process of transcription is a major source of DNA damage, due to the formation of single-strand DNA intermediates that are vulnerable to damage. [53] The regulation of transcription by processes using base excision repair and/or topoisomerases to cut and remodel the genome also increases the vulnerability of DNA to damage. [53]
Double-stranded RNA viruses (dsRNA viruses) are a polyphyletic group of viruses that have double-stranded genomes made of ribonucleic acid.The double-stranded genome is used as a template by the viral RNA-dependent RNA polymerase (RdRp) to transcribe a positive-strand RNA functioning as messenger RNA (mRNA) for the host cell's ribosomes, which translate it into viral proteins.