A brief look at transposons, an important element in the study of genetics.

1. Transposons the ‘Jumping Genes’ Abhranil Das 08MS34 Freshman 2009

2. Introduction Transposons are sections of the genome that undergo transposition within the genome of the same cell, which may cause mutations. Discovered by Barbara McClintock, for which she was awarded a Nobel prize in 1983. She observed how transposition in maize genome affected kernel colour. Transposons are now a hot favourite among biologists in the field of gene manipulation

3. Types of Transposon Type I: Retrotransposons Copy, Paste, Send to = transcription, reverse transcription, migration They have direct repeats at each end They show similarity with retroviruses like HIV. Mechanism of action also similar, except that transcription step is absent for viruses. Main enzymes required: transcriptase, reverse transcriptase

4. Action of Retrotransposons

5. Types of Transposon Type II: DNA-only transposons Cut, Paste = excision, staggered cut at target, ligation, polymerization Have inverted repeats at each end Main enzyme required: transposase No RNA intermediate

6. Action of DNA-only transposons

7. Action of DNA-only transposons

8. Action of DNA-only transposons

9. Action of DNA-only transposons

10. Transposons cause target repeats

11. Insertion Sequences: Self Sufficiency A transposon needs a transposase, an enzyme, for transposition A transposon which contains a sequence coding for such an enzyme is an insertion sequence It does not have to depend on whether the genome of the cell has a sequence elsewhere coding for the transposase enzyme.

12. Composite Transposons In addition to the IS, they contain other genetic information. This additional DNA is usually at the centre, flanked by the IS sequences on either side. May transpose in various ways

13. Credits Google Search http://www.google.com Wikipedia http://en.wikipedia.org/wiki/Transposon Microsoft Word Autoshape and Drawing Canvas tools