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Lecture Molecular biology - Chapter 23 introduce to transposition. This chapter presents the following content: Bacterial transposons, Eukaryotic transposons, rearrangement of immunoglobulin genes, retrotransposons. | Molecular Biology Fourth Edition Chapter 23 Transposition Lecture PowerPoint to accompany Robert F. Weaver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 23.1 Bacterial Transposons A transposable element moves from one DNA address to another Originally discovered in maize, transposons have been found in all kinds of organisms Bacteria Plants Humans 23- Discovery of Bacterial Transposons Phage coat is made of protein Always has the same volume DNA is much denser than protein More DNA in phage, denser phage Extra DNAs that can inactivate a gene by inserting into it were the first transposons discovered in bacteria These transposons are called insertion sequences (ISs) 23- Insertion Sequences Insertion sequences are the simplest type of bacterial transposon They contain only the elements necessary for their own transposition Short inverted repeats at their ends At least 2 genes coding for an enzyme, transposase that carries out . | Molecular Biology Fourth Edition Chapter 23 Transposition Lecture PowerPoint to accompany Robert F. Weaver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 23.1 Bacterial Transposons A transposable element moves from one DNA address to another Originally discovered in maize, transposons have been found in all kinds of organisms Bacteria Plants Humans 23- Discovery of Bacterial Transposons Phage coat is made of protein Always has the same volume DNA is much denser than protein More DNA in phage, denser phage Extra DNAs that can inactivate a gene by inserting into it were the first transposons discovered in bacteria These transposons are called insertion sequences (ISs) 23- Insertion Sequences Insertion sequences are the simplest type of bacterial transposon They contain only the elements necessary for their own transposition Short inverted repeats at their ends At least 2 genes coding for an enzyme, transposase that carries out transposition Transposition involves: Duplication of a short sequence in the target DNA One copy of this sequence flanks the insertion sequence on each side after transposition 23- Generating Host DNA Direct Repeats 23- Complex Transposons The term “selfish DNA” implies that insertion sequences and other transposons replicate at the expense of their hosts, providing no value in return Some transposons do carry genes that are valuable to their hosts, antibiotic resistance is among most familiar 23- Antibiotic Resistance and Transposons Donor plasmid has Kanr, harboring transposon Tn3 with Ampr Target plasmid has Tetr After transposition, Tn3 has replicated and there is a copy in target plasmid Target plasmid now confers both Ampr, Tetr 23- Transposition Mechanisms Transposons are sometimes called “jumping genes”, DNA doesn’t always leave one place for another When it does, nonreplicative transposition “Cut and paste” Both strands of original DNA move together from 1 place to .
