What is the Difference Between Composite and Non-composite Transposons

The main difference between composite and non-composite transposons is that composite transposons consist of two IS elements of the same type, bracketing one or more genes, whereas non-composite transposons consist of both transposition and non-transposition genes, clustering by terminal IR sequences.

Composite and non-composite transposons are two types of transposable elements. Generally, 50% of the human genome consists of transposons.  

Key Areas Covered

1. What are Composite Transposons
     – Definition, Structure, Function
2. What are Non-composite Transposons
     – Definition, Structure, Function
3. Similarities Between Composite and Non-composite Transposons
     – Outline of Common Features
4. Difference Between Composite and Non-composite Transposons
     – Comparison of Key Differences

Key Terms                                                                                                                  

Composite Transposons, Non-Composite Transposons

What are Composite Transposons

Composite transposons are protein-coding DNA segments flanked by inverted, repeated sequences. Generally, these sequences are insertion sequence (IS) elements. The size of the IS elements can range from 0.6 to 2.5 kbp. This means two IS elements flank the DNA segment that is protein-coding. Composite transposons consist of more than one gene that occurs in clusters. The main function of a transposon is to jump or change the positions within the genome. Some examples of composite transposons include Tn3, Tn5, and Tn10.

Figure 1: Tn3 Transposon

Furthermore, IS elements flank each DNA segment that moves separately. Therefore, each gene in the cluster of the composite transposon moves together from one to another location in the genome. In addition, a composite transposon contains an antibiotic-resistant gene carrying with other genes in the cluster. In a eukaryotic cell, transposons make up a large portion of the genome. They also create mutations by altering genetic identity and genome size. More often, transposons result in the duplication of genetic material.    

What are Non-Composite Transposons

Non-composite transposons or simple transposons are genes flanked by terminal inverted repeats (IR). Generally, IR sequences are single-stranded sequences of nucleotides. A downstream reverse complement follows the inverted repeat. Here, the intervening sequence that occurs between the initial sequence and the reverse complement can be any length from zero. Moreover, when the intervening length is zero, the composite sequence is called a palindromic sequence. In fact, 5′—TTACGnnnnnnCGTAA—3′ is an example of an inverted repeat sequence.  

Figure 2: piggyBac Transposon

However, IS elements do not flank the genes in the non-composite transposons. Simple transposons contain their own coding transposase and resolvase enzymes. Moreover, this transposase is responsible for the excision and transfer of the transposon. At the same time, resolvase is responsible for the resolution and transfer of the transposon, and a simple transposition is called a cut-and-paste transposition. Additionally, some examples of non-composite transpositions include piggyBac (PB), Tn5469, and Tn5541.

Similarities Between Composite and Non-composite Transposons

• Composite and non-composite transposons are two types of transposons that occur in the genome.
• Both of them move within the genome of a particular organism.
• Moreover, they are flanked by short, inverted, repeated sequences.
• Generally, both transposons have similar functions, changing the position within the genome.
• In addition, transposons are mutagenic.

Difference Between Composite and Non-composite Transposons

Definition

Composite transposons refer to transposons that consist of two inverted repeats from two separate transposons moving together as one unit and carrying the DNA between them, while non-composite transposons refer to gene clusters that are flanked by terminal IR sequences.

Genes

Composite transposons contain genes in clusters, while non-composite transposons contain separate genes.

Flanking

Insertion sequence (IS) elements flank composite transposons, while terminal inverted repeat (IR) sequences flank non-composite transposons.

Other Genes

Composite transposons contain antibiotic-resistant genes while non-composite transposons contain transposase enzyme.

Examples

Composite transposons include Tn5 and Tn10, while non-composite transposons include Tn5469 and Tn5541.

Conclusion                                                      

In brief, composite and non-composite transposons are two types of transposons that occur in the genome of both eukaryotes and prokaryotes. Generally, the main function of transposons is to change the position within the genome. Here, composite transposons contain genes in clusters. These genes are also flanked by two IS elements. In comparison, non-composite transposons contain individual genes flanked by IR sequences. Generally, they are also known as simple transposons. Therefore, the main difference between composite and non-composite transposons is gene clustering and flanking.                     

References:                

1. Schaefer MR, Kahn K. Cyanobacterial transposons Tn5469 and Tn5541 represent a novel noncomposite transposon family. J Bacteriol. 1998 Nov;180(22):6059-63. doi: 10.1128/JB.180.22.6059-6063.1998. PMID: 9811670; PMCID: PMC107686.

Image Courtesy:

1. “Replicative integration in Tn3 transposon” By Famedog – Own work (CC0) via Commons Wikimedia
2. “Lifecycle of the Piggybac Transposon System” By Transposagenbio – Own Work (CC0) via Commons Wikimedia