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Transposition
Wissenschaftliches Programm 55. DGHM-Tagung 29. September-1. Oktober 2003 in Dresden Abstracts- DFG-SSP-Statusseminar
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Transposition Chandler, M. 1
iLaboratoire de Microbiologie; Genomes are populated by discrete DNA segments whose capacity to translocate within and between replicons provides a powerful motor for generating large scale genetic diversity. These genetic objects are found in most eukaryote and prokaryote genomes and are themselves quite diverse. Some, such as plasmids and phage and other more exotic elements such as conjugative transposons, are capable of undergoing transfer between individuals and sometimes between species. Others rely on these transmissible elements for their dispersion. This talk will focus on one large class of mobile genetic element, the insertion sequences (ISs). These are small (0.7- 2.5kb) segments of DNA which include a single or sometimes two open reading frames (orf) which constitute nearly the entire length of the element and encode an enzyme, the transposase (Tpase), which catalyses the steps necessary for mobility. More than 1000 different ISs have been identified to date and this does not include many which have been revealed in the increasing number of sequenced bacterial genomes. They have been loosely divided into about 20 families. Their distribution, both in terms of number and type is highly variable from species to species. Some bacterial genomes may carry more than one hundred IS copies made up of members of different families and different members of the same family. The vast majority of ISs, like the retroviruses and many transposons, encode a Tpase which carries a characteristic constellation of amino acids called the DDE motif from three highly conserved residues which are involved in catalysis. The chemistry of the transposition reaction of these diverse elements must therefore be similar. However, the types of transposition product may vary from element to element. Some elements remain attached to donor DNA during transposition and their translocation results in a fusion between target and donor replicons. Other elements are separated from their flanking donor DNA prior to their insertion into a target site. This requires processing both strands at both ends of the element. While cleavage of the first strand may appear similar, recent results have shown that different strategies have been adopted for cleavage of the second, complementary, strand to liberate the transposon. An outline of these strategies will be presented together with an overview of the transposition mechanism adopted by one of the major IS families.
http://www.dghm.org
441
G~ ~ G ES~z
&NOMt~'JO~'\O
Transposition Chandler, M. 1
iLaboratoire de Microbiologie; Genomes are populated by discrete DNA segments whose capacity to translocate within and between replicons provides a powerful motor for generating large scale genetic diversity. These genetic objects are found in most eukaryote and prokaryote genomes and are themselves quite diverse. Some, such as plasmids and phage and other more exotic elements such as conjugative transposons, are capable of undergoing transfer between individuals and sometimes between species. Others rely on these transmissible elements for their dispersion. This talk will focus on one large class of mobile genetic element, the insertion sequences (ISs). These are small (0.7- 2.5kb) segments of DNA which include a single or sometimes two open reading frames (orf) which constitute nearly the entire length of the element and encode an enzyme, the transposase (Tpase), which catalyses the steps necessary for mobility. More than 1000 different ISs have been identified to date and this does not include many which have been revealed in the increasing number of sequenced bacterial genomes. They have been loosely divided into about 20 families. Their distribution, both in terms of number and type is highly variable from species to species. Some bacterial genomes may carry more than one hundred IS copies made up of members of different families and different members of the same family. The vast majority of ISs, like the retroviruses and many transposons, encode a Tpase which carries a characteristic constellation of amino acids called the DDE motif from three highly conserved residues which are involved in catalysis. The chemistry of the transposition reaction of these diverse elements must therefore be similar. However, the types of transposition product may vary from element to element. Some elements remain attached to donor DNA during transposition and their translocation results in a fusion between target and donor replicons. Other elements are separated from their flanking donor DNA prior to their insertion into a target site. This requires processing both strands at both ends of the element. While cleavage of the first strand may appear similar, recent results have shown that different strategies have been adopted for cleavage of the second, complementary, strand to liberate the transposon. An outline of these strategies will be presented together with an overview of the transposition mechanism adopted by one of the major IS families.
http://www.dghm.org
441