replicate using protein-primed DNA polymerases. Polintons have been proposed to go through a similar self-synthesis by their polymerase. Polintons, 15–20 kb long, encode up to 10 individual proteins. For replication, they utilize a protein-primed DNA polymerase B, retroviral integrase, cysteine protease, and ATPase. First, during host genome replication, a single-stranded extra-chromosomal Polinton element is excised from the host DNA using the integrase, forming a racket-like structure. Second, the Polinton undergoes replication using the DNA polymerase B, with initiation started by a terminal protein, which may encoded in some linear plasmids. Once the double stranded Polinton is generated, the integrase serves to insert it into the host genome. Polintons exhibit high variability between difference species and may tightly regulated, resulting in a low frequency rate in many genomes. Classification As of the most recent update in 2015, 23 superfamilies of DNA transposons were recognized and annotated in Repbase, a database of repetitive DNA elements maintained by the Genetic Information Research Institute: Effects of transposons DNA transposons, like all transposons, are quite impactful with respect to gene expression. A sequence of DNA may insert itself into a previously functional gene and create a mutation. This can happen in three distinct ways: 1. alteration of function, 2. chromosomal rearrangement, and 3. a source of novel genetic material. Since DNA transposons may happen to take parts of genomic sequences with them, exon shuffling may occur. Exon shuffling is the creation of novel gene products due to the new placement of two previously unrelated exons through transposition. Because of their ability to alter DNA expression, transposons have become an important target of research in genetic engineering. Examples Maize Barbara McClintock first discovered and described DNA transposons in Zea mays, during the 1940s; this is an achievement that would earn her the Nobel Prize in 1983. She described the Ac/Ds system where the Ac unit (activator) was autonomous but the Ds genomic unit required the presence of the activator in order to move. This TE is one of the most visually obvious as it was able to cause the maize to change color from yellow to brown/spotted on individual kernels. Fruit flies The Mariner/Tc1 transposon, found in many animals but studied in Drosophila was first described by Jacobson and Hartl. Mariner is well known for being able to excise and insert horizontally in to a new organism. Thousands of copies of the TE have been found