Concatemer
Type of DNA molecule
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Related on Lably
During active infection, some species of viruses have been shown to replicate their genetic material via the formation of concatemers. In the case of human herpesvirus-6, its entire genome is made over and over on a single strand. These long concatemers are subsequently cleaved between the pac-1 and pac-2 regions by ribozymes when the genome is packaged into individual virions.
Bacteriophage T4 replicating DNA was labeled with tritiated thymidine and examined by autoradiography. The observed DNA replication intermediates included circular and branched circular concatemeric structures that likely arose by rolling circle replication.
When assembling concatemers from synthetic oligonucleotides, increasing salt concentration to 200 mM was found to be a major optimizing factor due to its ability to enhance ionic strength, which hastened the formation of concatemers.
Mechanism/ replication
In addition to rolling circle replication, many DNA viruses employ recombination-dependent replication to produce concatemers. In this mechanism, replication is initiated at multiple sites, followed by strand invasion and homologous recombination, which join replication forks and generate long tandem repeats. Some viruses initiate multiple consecutive reinitiation events at genomic termini, which lead to overlapping replication rounds that effectively result in concatemer formation.
Concatemers, especially when unresolved, can contribute to genomic instability and rearrangements. Tandem duplication, unequal, crossover, and insertion/deletion may occur. Over time, concatemers may seed new tandem repeat arrays or satellite DNA, and in viruses, variation in concatemer length can drive genetic diversity.
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Mitochondria
In yeast S. cerevisiae concatamers are an essential part of the process for packaging DNA. We know this because of experiments done on the yeast S cerevisiae cells.
-There are two ways that concatamers are formed, rolling circle replication and crossing over.
-Mhr1 is a protein that starts the rolling circle replication for mitochondrial DNA in the yeast.
-CCE1 is a protein that helps with crossing over.
-If the gene for Mhr1 is overexpressed there will be more concatamers, if it is disrupted by a mutation there will be less concatamers.
-If both the MHR1 gene and CCE1 genes are disrupted by mutations concatamers won’t be able to form and the cell will have no mitochondrial DNA. Mitochondrial DNA won't form without concatamers. That proves that they are necessary for mitochondrial DNA.
Rolling Circle DNA Replication
One of the ways concatamers are formed is through rolling circle replication. In rolling circle replication the outer strand of DNA is cut at an origin. That strand is peeled off of it’s complementary strand. As it is fully peeled off, DNA replicase will attach nucleotides to the inner strand to replace the peeled strand. Once the strand is fully peeled DNA replicase can bind nucleotides so that it will have a complementary strand. After the process, there will be two strands of DNA with their complements.