RNA genome

(noun)

Like DNA, RNA can carry genetic information. RNA viruses have genomes composed of RNA that encodes a number of proteins.

Examples of RNA genome in the following topics:

  • Double-Stranded RNA Viruses: Retroviruses

    • Retroviruses are viruses that are able to reverse transcribe their RNA genome into DNA, which is then integrated into a host genome.
    • A retrovirus is an RNA virus that is duplicated in a host cell using the reverse transcriptase enzyme to produce DNA from its RNA genome.
    • The virus itself stores its nucleic acid in the form of an mRNA genome and serves as a means of delivering that genome into cells it targets as an obligate parasite (a parasite that cannot live without its host).
    • Once in the host's cell, the RNA strands undergo reverse transcription in the cytoplasm and are integrated into the host's genome, at which point the retroviral DNA is referred to as a provirus.
    • In most viruses, DNA is transcribed into RNA, and then RNA is translated into protein.

  • Viral Genomes

    • The viral genome is the complete genetic complement contained in a DNA or RNA molecule in a virus.
    • A virus has either DNA or RNA genes and is called a DNA virus or a RNA virus, respectively.
    • The vast majority of viruses have RNA genomes.
    • Plant viruses tend to have single-stranded RNA genomes and bacteriophages tend to have double-stranded DNA genomes.
    • Among RNA viruses and certain DNA viruses, the genome is often divided up into separate parts, in which case it is called segmented.

  • RNA Bacteriophages

    • Nineteen families of bacteriophages that infect bacteria and archaea are currently recognized; of these, only two families have RNA genomes.
    • Of these, only two families have RNA genomes: Cystoviridae (segmented dsRNA) and Leviviridae (linear ssRNA).
    • Cystovirus is a genus of dsRNA virus that infect certain Gram-negative bacteria.
    • It has a three-part, segmented, double-stranded RNA genome, totalling ~13.5 kb in length.
    • RNA-dependent RNA polymerases (RdRPs) are critical components in the life cycle of double-stranded RNA (dsRNA) viruses.

  • Viral Identification

    • DNA viruses: The genome replication of most DNA viruses takes place in the cell's nucleus.
    • Most DNA viruses are entirely dependent on the host cell's DNA and RNA synthesizing machinery and RNA processing machinery; however, viruses with larger genomes may encode much of this machinery themselves.
    • All RNA viruses use their own RNA replicase enzymes to create copies of their genomes.
    • Reverse transcribing viruses with RNA genomes (retroviruses), use a DNA intermediate to replicate, whereas those with DNA genomes (pararetroviruses) use an RNA intermediate during genome replication.
    • Reoviruses)IV: (+)ssRNA viruses (+)sense RNA (e.g.

  • Viral Replication and Gene Expression

    • RNA viruses are classified into distinct groups depending on their genome and mode of replication.
    • Replication of viruses primarily involves the multiplication of the viral genome.
    • Replication also involves synthesis of viral messenger RNA (mRNA) from "early" genes (with exceptions for positive sense RNA viruses), viral protein synthesis, possible assembly of viral proteins, then viral genome replication mediated by early or regulatory protein expression.
    • No viral proteins can be made until viral messenger RNA is available; thus, the nature of the RNA in the virion affects the strategy of the virus: In plus-stranded RNA viruses, the virion (genomic) RNA is the same sense as mRNA and so functions as mRNA.
    • RNA viruses are classified into distinct groups depending on their genome and mode of replication (and the numerical groups based on the older Baltimore classification).

  • RNA Oncogenic Viruses

    • Specifically, RNA viruses have RNA as their genetic material and can be either single-stranded RNA (ssRNA) or double-stranded (dsRNA).
    • Retroviruses are different from DNA tumor viruses in that their genome is RNA, but they are similar to many DNA tumor viruses in that the genome is integrated into host genome.
    • Since RNA makes up the genome of the mature virus particle, it must be copied to DNA prior to integration into the host cell chromosome.
    • Gag-encoded proteins also coat the genomic RNA.
    • There are two molecules of genomic RNA per virus particle with a 5' cap and a 3' poly A sequence.

  • Positive-Strand RNA Viruses of Animals

    • Positive strand RNA viruses are the single largest group of RNA viruses with 30 families.
    • Single stranded RNA viruses can be classified according to the sense or polarity of their RNA into negative-sense and positive-sense, or ambisense RNA viruses.
    • Negative-sense viral RNA is complementary to mRNA and thus must be converted to positive-sense RNA by an RNA polymerase before translation.
    • The genome RNA is unusual because it has a protein on the 5' end that is used as a primer for transcription by RNA polymerase.
    • The name is derived from pico, meaning small, and RNA, referring to the ribonucleic acid genome, so "picornavirus" literally means small RNA virus.

  • Replicative Cycle of Influenza A

    • Delivering the genome to a site where it can produce new copies of viral proteins and RNA
    • It is known that virions converge to the microtubule organizing center, interact with acidic endosomes, and finally enter the target endosomes for genome release.
    • The viral RNA (vRNA) molecules, accessory proteins, and RNA-dependent RNA polymerase are then released into the cytoplasm (Step 2 in figure).
    • Newly synthesized viral proteins are either secreted through the Golgi apparatus onto the cell surface (in the case of neuraminidase and hemagglutinin, Step 5b) or transported back into the nucleus to bind vRNA and form new viral genome particles (Step 5a).
    • Negative-sense vRNAs that form the genomes of future viruses, RNA-dependent RNA polymerase, and other viral proteins are assembled into a virion.

  • Retroviruses and Hepadnavirus

    • Instead of using the RNA for templates of proteins, they use DNA to create the templates, which is spliced into the host genome using integrase.
    • The virus itself stores its nucleic acid in the form of a +mRNA (including the 5'cap and 3'PolyA inside the virion) genome.
    • Once in the host's cell, the RNA strands undergo reverse transcription in the cytoplasm and are integrated into the host's genome, at which point the retroviral DNA is referred to as a provirus.
    • In most viruses, DNA is transcribed into RNA, and then RNA is translated into protein.
    • The genome consists of two uneven strands of DNA.

  • Noncoding DNA

    • Some noncoding DNA is transcribed into functional noncoding RNA molecules (e.g. transfer RNA, ribosomal RNA, and regulatory RNAs), while others are not transcribed or give rise to RNA transcripts of unknown function.
    • For example, over 98% of the human genome is noncoding DNA, while only about 2% of a typical bacterial genome is noncoding DNA.
    • The amount of total genomic DNA varies widely between organisms, and the proportion of coding and noncoding DNA within these genomes varies greatly as well.
    • The pufferfish Takifugu rubripes genome is only about one eighth the size of the human genome, yet seems to have a comparable number of genes; approximately 90% of the Takifugu genome is noncoding DNA.
    • In 2013, a new "record" for most efficient genome was discovered.