Ac/Ds Activator/Dissociation Transposable Element
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The Ac/Ds transposable element system of maize was first discovered by Barbara McClintock, leading to her 1983 Nobel Prize in Medicine. The Ac Activator element is autonomous, whereas the Ds Dissociation element requires an Activator element to transpose. Ac was initially discovered as enabling a Ds element to break chromosomes. Both Ac and Ds can also insert into genes, causing mutants that may revert to normal on excision of the element. These elements were first isolated and sequenced By Federoff et al. 1983  using insertions of Ac and Ds into the well-studied Waxy(Wx1) gene.
Genomic analysis of maize show that these elements, which share terminal 11 bp inverted repeat sequences, have much sequence heterogeneity, both in length and content. They also include a class of DNA elements that do not transpose in the presence of the Ac element (Du et al. 2011). The chromosome breaking property has been shown to come from pairs of closely positioned elements, reviewed by Huang and Dooner 2008.
Researchers use mutant phenotypes to discover gene functions. Ac/Ds prefer to transpose to nearby genes, affording a way to mutagenize those regions of the genome, and by subsequent genetic crosses, remove the Ac that causes new mutants and instability of a Ds mutant. Collections of Ac/Ds elements that cover the genome and are useful for generating mutants have been described by Vollbrect et al. An additional collection, that involves Chromosome Breaking Ds elements has been collected by M Gerald Neuffer, and information and images provided to MaizeGDB. With his permission, this collection of images is provided to the Wikipedia.
Chromosome breaking examples
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- McClintock, Barbara (1947). "Cytogenetic studies of maize and Neurospora". Carnegie Inst. Washington Year Book. 46: 146–152.
- McClintock, Barbara (1949). "Mutable loci in maize.". Carnegie Inst. Washington Year Book. 48: 142–154.
- McCLINTOCK, B (June 1950). "The origin and behavior of mutable loci in maize.". Proceedings of the National Academy of Sciences of the United States of America. 36 (6): 344–55. doi:10.1073/pnas.36.6.344. PMC . PMID 15430309.
- Fedoroff, N; Wessler, S; Shure, M (November 1983). "Isolation of the transposable maize controlling elements Ac and Ds.". Cell. 35 (1): 235–42. doi:10.1016/0092-8674(83)90226-x. PMID 6313225.
- Baker, B; Coupland, G; Fedoroff, N; Starlinger, P; Schell, J (June 1987). "Phenotypic assay for excision of the maize controlling element Ac in tobacco.". The EMBO Journal. 6 (6): 1547–54. PMID 16453771.
- Van Sluys, MA; Tempé, J; Fedoroff, N (Dec 20, 1987). "Studies on the introduction and mobility of the maize Activator element in Arabidopsis thaliana and Daucus carota.". The EMBO Journal. 6 (13): 3881–9. PMID 2832144.
- Murai, N; Li, ZJ; Kawagoe, Y; Hayashimoto, A (Feb 11, 1991). "Transposition of the maize activator element in transgenic rice plants.". Nucleic Acids Research. 19 (3): 617–22. doi:10.1093/nar/19.3.617. PMID 1849265.
- Huang, JT; Dooner, HK (August 2008). "Macrotransposition and other complex chromosomal restructuring in maize by closely linked transposons in direct orientation.". The Plant cell. 20 (8): 2019–32. doi:10.1105/tpc.108.060582. PMID 18708475.
- Vollbrecht, E; Duvick, J; Schares, JP; Ahern, KR; Deewatthanawong, P; Xu, L; Conrad, LJ; Kikuchi, K; Kubinec, TA; Hall, BD; Weeks, R; Unger-Wallace, E; Muszynski, M; Brendel, VP; Brutnell, TP (June 2010). "Genome-wide distribution of transposed Dissociation elements in maize.". The Plant cell. 22 (6): 1667–85. doi:10.1105/tpc.109.073452. PMID 20581308.