Transposable Element | an Over view and Classification of TE based on method of transposition

What are Transposable Elements (TEs)

By Meet Patel

(image1. how the jumping gene involves the phenotype of an organism. Barbara McClintock studied the jumping gene in Zea mays (maize) in 1948.)

Introduction

Many different kinds of transposable elements have been identified in an assortment of organisms, including bacteria, fungi, protists, plants, and animals. The first Transposable Element was discovered in maize by Barbara McClintock in 1948. She observed insertion, deletion, and translocation by these elements. transposable elements are prominent components of the genome (may be >40%)and they have crucial roles in shaping the structure of chromosomes and regulation of the gene. Each kind of Transposons has its special characteristics. They can be classified into three categories. (classification is given in the following image.)

(table 1. categories of a transposable element.)

CUT-PASTE TRANSPOSONS

(image2. TE transposition via excision and insertion into a site other than the original site on the chromosome.)

In this type of transposable element, a transposition is accomplished via excising an element from its position in a chromosome and inserting it into the other position of may the same chromosome or may another chromosome. Both the events, excising and insertion, are catalyzed by an enzyme called "Transposase" which is usually coded by transposable elements themselves. Because of the excision, the element cut out from their original position and inserted into the other position, like the cut and paste process, these elements include in the CUT-PASTE TRANSPOSONS category.

REPLICATIVE TRANSPOSONS

(image3. TE transposition via synthesis of new TE and then insert it into another site on the chromosome.)

In this type of transposable element, a transposition is accomplished via a process that involves replication of the transposable element and a new copy of the element inserted into the other side of the chromosome. Replicative transposons encode two different enzymes, in which one is transposase help in transposition and the other is resolvase help in regulation and function of the element. Because of the making new element, this type of transposons are increase genomic contain and this new element inserts into the site other than the original site on the chromosome, like copy and paste process, this element includes into REPLICATIVE/ COPY-PASTE TRANSPOSONS category.

RETROTRANSPOSONS

(image4. TE transposition via reverse transcription to produce cDNA as TE and then insertion of TE into another site on the chromosome.)

In this type of transposable element, a transposition is accomplished via a process that involves reverse transcription. These elements are RNA molecule which is not able to insert directly into the chromosome. They have to reverse transcribe into DNA molecule (cDNA) and then insert into the chromosome. Retroposons encode two different enzymes, in which one is reverse transcriptase help to synthesize complementary DNA (cDNA) and the other is transposase help in the transposition of the element (cDNA). Because the element is an RNA molecule and they have to reverse transcribed into cDNA and then translate in the chromosome, this element includes in the RETROTRANSPOSONS/ RETROPOSONS category.