Transposons2.pptx

transposon, class of genetic elements that can “jump” to different locations within a genome. Although these elements are frequently called “jumping genes,” they are always maintained in an integrated site in the genome. In addition, most transposons eventually become inactive and no longer move.1

1. Dr. Rachana Choudhary Department of Microbiology Shri Shankaracharya Mahavidyalaya , Junwani , Bhilai

2. SYNOPSIS Introducton Discovery Of Transposons Types Of Transposonson -DNA Transposons - Retrotransposons Bacterial Transposons -Insertion Sequence -Composite Transposons - Tn -type Transposons Mechanism of Transposition 1.Replicative 2.Non Replicative Disease Caused by Transposition Application Conclusion Reference

3. INTRODUCTION Transposon , class of genetic elements that can “jump” to different locations within a genome. Although these elements are frequently called jumping genes , Transposable elements , Mobile DNA and are always maintained in an integrated site in the genome. In addition, most transposons eventually become inactive and no longer move. able to move from one place to another within a cell’s genome sometimes a copy is made and the copy Moves insertion requires target DNA sequences

4. In this process, it may - Cause Mutations. - Increase (Or Decrease) The Amount of DNA in The Genome. - Promote Genome Rearrangements. - Regulate Gene Expression. - Induce Chromosome Breakage and Rearrangement .

5. Discovery of transposons Barbara McClintock 1950’s Ac Ds system in maize influencing kernel color unstable elements changing map position promote chromosomal breaks . Rediscovery of bacterial insertion sequences source of polar mutations discrete change in physical length of DNA inverted repeat ends: form “lollipops ” in EM after denaturation. These mobile segments of DNA are sometimes called "jumping genes“

6. TYPES OF TRANSPOSONS There are two distinct types of transposons: 1) DNA transposons transposons consisting only of DNA that moves directly from place to place 2) Retrotransposons - first transcribe the DNA into RNA and then - use reverse transcriptase to make a DNA copy of the RNA to insert in a new location

7. Classification of Transposons into two classes In both cases ds DNA intermediate is integrated into the target site in DNA to complete movement In both cases ds DNA intermediate is integrated into the target site in DNA to complete Movement.

8. BACTERIAL TRANSPOSONS In bacteria , transposons can jump from chromosomal DNA to plasmid DNA and back. Transposons in bacteria usually carry an additional gene for function other than transposition often for antibiotic resistance . Bacterial transposons of this type belong to the Tn family. When the transposable elements lack additional genes, they are known as insertion sequences.

9. TYPES of BACTERIAL TRANSPOSONS 1.Insertion sequence 2.Composite transposon 3.Tn3-type transposon

10. 1.Insertion Sequences Insertion sequences – IS1 and IS186, present in the 50- kb segment of the E.coli DNA, are examples of DNA transposons. Single E. coli genome may contain 20 of them. Most of the sequence is taken by one or two genes for transposase enzyme that catalyses transposition. IS elements transpose either replicatively or conservatively. Study of E. coli mutations resulting from insertion of 1-2 kb long sequence in the middle of certain genes. Inserted stretches or insertion sequences – could be visualized by EM. IS - molecular parasites in bacterial cells. Transposition of IS is very rare – one in 105-107 cells per generation. Higher rates result in greater mutation rates.

11. Bacterial IS element Central region encodes for one or two enzymes required for transposition. It is flanked by inverted repeats of characteristic sequence. The 5’ and 3’ short direct repeats are generated from the target-site DNA during the insertion of mobile element. The length of these repeats is constant for a given IS element, but their sequence depends upon the site of insertion and is not characteristic for the IS element.Arrows indicate orientation

12. Insertion sequences in E.coli Elements Size ( bp ) No. of.Copies /Genome IS1 768 8 IS2 1327 5 IS3 1300 1 or more IS4 1426 1 or more

13. 2.Composite transposons Bacteria contain composite mobile genetic elements that are larger than IS elements and contain 1 or more protein-coding genes in addition to those required for transposition: Composite transposons - are basically the pair of IS elements flanking a segment of DNA usually containing one or more genes, often coding for Antibiotic resistance. They use conservative method of transposition.

14. 2.Composite transposon - Antibiotic resistant gene - Flank by IS element ( inverted or directed repeat) - Terminal IS can transpose by in self Ex. Tn5, Tn9, Tn10

15. 3. Tn3 transposon family 5000 bp Code for Transposase , β- lactamase, Resolvase Function of resolvase decrease Transposase production Catalyze the recombination of transposon

16. Mechanism of transposition Two distinct mechanisms of transposition: 1.Replicative transposition – direct interaction between the donor transposon and the target site, resulting in copying of the donor element 2.Conservative transposition – involving excision of the element and reintegration at a new site.

17. 1. Replicative transposition Copy of transposon sequence Transposase enzyme cut target DNA Transposition Duplication of target sequence

18. Replicative transposition

19. 2. Non- replicative (conservative) transposition - Cannot copy transposon sequence -Transposition by cut and paste model Cut transposon sequence from donor molecule attach to target site Ex. IS10, Tn10

20. Non- replicative (conservative) transposition

21. Mechanism of transposition

22. Transposons causing diseases Transposons are mutagens. They can damage the genome of their host cell in different ways : 1 . A transposon or a retrotronsposon that inserts itself into a functional gene will most likely disable that gene. 2. After a transposon leaves a gene, the resulting gap will probably not be repaired correctly. 3. Multiple copies of the same sequence, such as Alu sequences can hinder precise chromosomal pairing during mitosis and meiosis , resulting in unequal crossovers, one of the main reasons for chromosome duplication.

23. Diseases caused by transposons include - Hemophilia A and B -Severe combined immunodeficiency - Porphyria - Cancer - Duchenne muscular dystrophy

24. Applications The first transposon was discovered in the plant maize ( Zea mays, corn species), and is named dissociator (Ds). Likewise , the first transposon to be molecularly isolated was from a plant (Snapdragon). Transposons have been an especially useful tool in plant molecular biology. Researchers use transposons as a means of mutagenesis. To identifying the mutant allele. To study the chemical mutagenesis methods . To study gene expression. Transposons are also a widely used tool for mutagenesis of most experimentally tractable organisms.

25. CONCLUSION The genomes of nearly all organisms contain mobile genetic elements that can move from one position in the genome to another by either transposons or conservative Site- specifc combination processes. In most cases this movement is random and happens at a very low frequency. Mobile genetic elements include transposons , which move within a single cell (and its descendants) plus those viruses whose genomes can integrate into the genomes of their host cells. A common feature of all mobile elements is the presence of short direct repeats flanking the sequence. Mobile DNA elements that transpose to new sites directly as DNA are called DNA transposons; those that first are transcribed into an RNA copy of the element, which is then reverse-transcribed into DNA, are called retrotransposons .

26. REFERENCE Microbiology by Dubey & Maheshwari Biotechnology by R.C. Dubey Molecular Cell Biology Lodish , 5 th edition Molecular Biology of the cell Alberts , 5 th edition

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