2-10-11 Transposition _ VDJ rec(1)

- Transposition Pathways Transposition(Part II and Immune Recombination Many transposable elements have been found in bacteria fungi plant and

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1 Transposition (Part II) and Immune Recombination February 10, 2011 Many transposable elements have been found in bacteria, fungi, plant and animal cells Three general types of transposition pathways have been identified: 1. Simple transposition 2. Replicative transposition 3. Retro-transposition Transposition Pathways This mechanism also called “cut-and-paste transposition. The transposing element (TE) remains in the form of DNA when it moves. It is widely found in bacteria and eukaryotes. Simple Transposition This mechanism involves replication of the TE and insertion of the new copy into another chromosomal location. Again, the TE remains in the form of DNA when it moves. It is relatively uncommon and only known in bacteria. Replicative Transposition
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2 This mechanism is very common in eukaryotes, but has not been found in bacteria, so far. In retro-transposition, the TE moves via an RNA intermediate . These types of elements are termed "retro-elements" , "retro- transposons" , or "retroposons". Retro-transposition Transposable Elements Have Characteristic DNA Structures The differing transposition mechanisms used by transposons are a consequence of: • their structural organization at the DNA sequence level, and… • the enzymes they encode. It is these features that define the different types or classes of transposable elements. The simplest type of TEs Direct repeats Found within the host DNA Catalyzes the transposition event Inverted repeats Length ranges from 9 to 40 bp Inverted repeats are DNA sequences that are identical (or very similar) but run in opposite directions, such as 5’ CTGACTCTT 3’ 3’ GACTGAGAA 5’ 5’ AAGAGTCAG 3’ 3’ TTCTCAGTC 5’ and Structure of a simple transposon Contain additional genes that are not necessary for transposition per se, but confer some selective advantage on the host. Probably derived from a coding gene captured between two simple transposons. Only the two inverted repeats nearest to the ends of the transposon are involved in the transposition event. Structure of a composite transposon
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3 Organization is similar to simple insertion sequences, except that a resolvase gene is (usually) found between the inverted repeats, in addition to transposase. Both enzymes are needed to catalyze the movement of replicative transposons. Structure of a replicative transposon The organization of retroelements can be quite variable depending on type; two major classes are known. One class bears a close relationship to retroviruses - RNA viruses that make a DNA copy that integrates into the host’s genome. Structure of a
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This note was uploaded on 04/04/2011 for the course GENETICS 385 taught by Professor Brennemanandgordon during the Spring '11 term at Rutgers.

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- Transposition Pathways Transposition(Part II and Immune Recombination Many transposable elements have been found in bacteria fungi plant and

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