The key difference between composite transposons and IS elements is that composite transposons are a type of transposons that carry accessory genes such as antibiotic resistance genes, while IS elements (or Insertion Sequence elements) are transposable elements that carry only genes that code transposase that catalyze the transposition activity.
A transposon is a fragment of DNA that can change its position within the bacterial genome. Therefore, they are mobile DNA sequences. They move into new locations of the genome, making changes in the sequence of the bacterial genome, causing significant changes in genetic information. Transposons are also known as jumping genes since they can block the transcription of genes and rearrange the genetic material of the bacterium. Moreover, they are responsible for the movement of drug resistance, antibiotic resistance genes between plasmids and chromosomes. Composite transposons and IS elements are two types of mobile genetic elements found in bacteria. Both can move from one location to another in the genome.
CONTENTS
1. Overview and Key Difference
2. What are Composite Transposons
3. What are IS Elements
4. Similarities Between Composite Transposons and IS Elements
5. Side by Side Comparison – Composite Transposons vs IS Elements in Tabular Form
6. Summary
What are Composite Transposons?
A composite transposon is a segment of DNA flanked by two copies of similar insertion sequence elements. There is a central protein-coding region in composite transposon. The genes are often antibiotic-resistant genes. They also can contain catabolic genes. Moreover, composite transposon consists of two inverted repeats. The entire length of the composite transposon moves as one complete unit.
Figure 01: Composite Transposon
Tn10 is a composite transposon. It consists of a 6.5 kb central coding region (tetracycline-resistant gene) and 1.4 kb inverted insertion sequence elements at each end. IS elements supply transposase. Transposase is an enzyme that catalyzes the movement of the transposon. Composite transposons can be amplified, designing primers for IS elements.
What are IS Elements?
Insertion sequence elements or IS elements are a type of mobile genetic element. They are a simple form of transposons. They carry only the genes coding for transposase enzymes. Transposase enzymes catalyze the transposition of transposons. Structurally, the coding sequence of IS elements is flanked by two inverted repeats. For example, IS element called IS911 is flanked by two 36bp inverted repeat extremities.
IS elements are the most abundant autonomous transposable elements in the bacterial genome. Hence, they are extremely important for prokaryotic genome organization and evolution. Furthermore, IS elements occur as parts of composite transposons. Generally, two IS elements are found flanking the coding sequence of the composite transposon. But, unit transposons do not carry flanking IS elements.
Since IS elements can move within the genome, they can interrupt the coding sequence of other genes and inactivate the genes by blocking expression.
What are the Similarities Between Composite Transposons and IS Elements?
- Both composite transposons and IS elements are able to change the position in the bacterial genome.
- The coding region in both transposons is usually flanked by inverted repeats.
- A composite transposon is flanked by two separate IS elements.
What is the Difference Between Composite Transposons and IS Elements?
Composite transposons are mobile genetic elements consisting of two insertion sequences (ISs) often flanking one or more antibiotic resistance genes. On the other hand, IS elements are a type of simple transposable element that contains genes coding for transposase enzyme to catalyze transposition. So, this is the key difference between composite transposons and IS elements.
Below is a list of differences between composite transposons and IS elements in tabular form for side by side comparison.
Summary – Composite Transposons vs IS Elements
A bacterial genome has genetic elements that are mobile. Composite transposons and IS elements are two types of mobile genetic elements. Composite transposons carry antibiotic-resistant genes and flanking IS elements. IS elements carry the genetic code to produce transposase which catalyzes the movement of transposons. Thus, this is the key difference between composite transposons and IS elements.
Reference:
1. Tansirichaiya, Supathep, et al. “PCR-Based Detection of Composite Transposons and Translocatable Units from Oral Metagenomic DNA.” FEMS Microbiology Letters, Oxford University Press, Sept. 2016, Available here.
2. Griffiths, Anthony JF. “Bacterial Insertion Sequences.” An Introduction to Genetic Analysis. 7th Edition., U.S. National Library of Medicine, 1 Jan. 1970, Available here.
Image Courtesy:
1. “Composite transposon” By Jacek FH – self-made, based on Image:Composite transposon.jpg (CC BY-SA 3.0) via Commons Wikimedia