genome fusion

(noun)

a result of endosymbiosis when a genome consists of genes from both the endosymbiont and the host.

Related Terms

Examples of genome fusion in the following topics:

  • Endosymbiotic Theory and the Evolution of Eukaryotes

    • Genome fusion occurs during endosymbiosis, which is the mechanism proposed as responsible for the first eukaryotic cells.
    • Scientists believe the ultimate event in HGT (horizontal gene transfer) occurs through genome fusion between different species when two symbiotic organisms become endosymbiotic.
    • Within the past decade, the process of genome fusion by endosymbiosis has been proposed to be responsible for the evolution of the first eukaryotic cells .
    • More controversial is the proposal that (a) the eukaryotic nucleus resulted from the fusion of archaeal and bacterial genomes; and that (b) Gram-negative bacteria, which have two membranes, resulted from the fusion of Archaea and Gram-positive bacteria, each of which has a single membrane.
    • Describe the genome fusion hypothesis and its relationship to the evolution of eukaryotes

  • Genomic Similiarities between Distant Species

    • Genomic similarities between distant species can be established via analysis of genomes using advanced technology.
    • These technologies have established genomic similarities between distant species by establishing genetic distances .
    • In addition, the mechanisms by which genomic similarities between distant species occur can include horizontal gene transfer.
    • Finally, as an example of the ultimate gene transfer, theories of genome fusion between symbiotic or endosymbiotic organisms have been proposed to explain an event of great importance—the evolution of the first eukaryotic cell, without which humans could not have come into existence.
    • Discuss the evolutionary implications of observed genome similarities between distant species

  • Viral Identification

    • DNA viruses: The genome replication of most DNA viruses takes place in the cell's nucleus.
    • If the cell has the appropriate receptor on its surface, these viruses sometimes enter the cell by direct fusion with the cell membrane (e.g., herpesviruses) or, more usually, by receptor-mediated endocytosis.
    • 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.
    • Pararetroviruses do not, although integrated genome copies, usually of plant pararetroviruses, can give rise to infectious virus.

  • Virus Attachment and Genome Entry

    • Attachment to the receptor can induce the viral envelope protein to undergo changes that results in the fusion of viral and cellular membranes, or changes of non-enveloped virus surface proteins that allow the virus to enter.
    • Penetration follows attachment: Virions enter the host cell through receptor-mediated endocytosis or membrane fusion.
    • However, given that bacterial cell walls are less thick than plant cell walls due to their much smaller size, some viruses have evolved mechanisms that inject their genome into the bacterial cell across the cell wall, while the viral capsid remains outside

  • HIV Attachment and Host Cell Entry

    • The attachment and fusion of HIV virons to host cells are crucial to HIV infection.
    • The first step in fusion begins after the attachment of the CD4 binding domains of gp120 to CD4.
    • This allows for a more stable two-pronged attachment, which allows the N-terminal fusion peptide gp41 to penetrate the cell membrane.
    • Steps in the HIV Replication Cycle: Fusion of the HIV cell to the host cell surface.Cell Entry, HIV RNA, reverse transcriptase, integrase, and other viral proteins enter the host cell.Viral DNA is formed by reverse transcription.Viral DNA is transported across the nucleus and integrates into the host DNA.New viral RNA is used as genomic RNA to make viral proteins.New viral RNA and proteins move to cell surface and a new, immature, HIV virus forms.Virus maturation and protease release of individual HIV proteins.
    • The attachment and fusion of HIV virons to host cells are crucial to allowing HIV infection to occur.

  • General Features of Virus Replication

    • Attachment to the receptor can fore the viral envelope protein to undergo either changes that result in the fusion of viral and cellular membranes, or changes of non-enveloped virus surface proteins that allow the virus to enter.
    • Virions enter the host cell through receptor-mediated endocytosis or membrane fusion.
    • In either case the end-result is the release of the viral genomic nucleic acid.
    • Replication of viruses depends on the multiplication of the genome.
    • Whenever the host divides, the viral genome is also replicated.

  • Fertilization

    • The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum.
    • Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte.
    • The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome.

  • Retroviral RNA Genome

    • The retroviral genome contains the elements needed for reverse transcription and all other activities of a retrovirus.
    • The RNA genome also has terminal noncoding regions, which are important in replication, and internal regions that encode virion proteins for gene expression.
    • The L region is an untranslated leader region that give the signal for packaging of genome RNA.
    • The ability of the retrovirus to bind to its target host cell using specific cell-surface receptors is given by the surface component (SU) of the env, while the ability of the retrovirus to enter the cell via membrane fusion is imparted by the membrane-anchored trans-membrane component (TM).
    • Through the mechanism of reverse transcription by human immunodeficiency virus (HIV), we see what the different genomic elements of a retrovirus are.

  • Animal Viruses

    • The viral genome is then "injected" into the host cell through these channels in a manner analogous to that used by many bacteriophages.
    • Enveloped viruses also have two ways of entering cells after binding to their receptors: receptor-mediated endocytosis and fusion.
    • On the other hand, fusion only occurs with enveloped virions.
    • These viruses, which include HIV among others, use special fusion proteins in their envelopes to cause the envelope to fuse with the plasma membrane of the cell, thus releasing the genome and capsid of the virus into the cell cytoplasm.
    • After making their proteins and copying their genomes, animal viruses complete the assembly of new virions and exit the cell.

  • 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).
    • It has a three-part, segmented, double-stranded RNA genome, totalling ~13.5 kb in length.
    • Fusion of the viral envelope with the bacterial outer membrane is facilitated by the phage protein, P6.