<P> Like DNA, RNA can carry genetic information . RNA viruses have genomes composed of RNA that encodes a number of proteins . The viral genome is replicated by some of those proteins, while other proteins protect the genome as the virus particle moves to a new host cell . Viroids are another group of pathogens, but they consist only of RNA, do not encode any protein and are replicated by a host plant cell's polymerase . </P> <P> Reverse transcribing viruses replicate their genomes by reverse transcribing DNA copies from their RNA; these DNA copies are then transcribed to new RNA . Retrotransposons also spread by copying DNA and RNA from one another, and telomerase contains an RNA that is used as template for building the ends of eukaryotic chromosomes . </P> <P> Double - stranded RNA (dsRNA) is RNA with two complementary strands, similar to the DNA found in all cells . dsRNA forms the genetic material of some viruses (double - stranded RNA viruses). Double - stranded RNA such as viral RNA or siRNA can trigger RNA interference in eukaryotes, as well as interferon response in vertebrates . </P> <P> In the late 1970s, it was shown that there is a single stranded covalently closed, i.e. circular form of RNA expressed throughout the animal and plant kingdom (see circRNA). circRNAs are thought to arise via a "back - splice" reaction where the spliceosome joins a downstream donor to an upstream acceptor splice site . So far the function of circRNAs is largely unknown, although for few examples a microRNA sponging activity has been demonstrated . </P>

Where are the different types of rna located