The key difference between LINEs and SINEs is that LINEs (long interspersed nuclear elements) are a type of longer non-LTR retrotransposons while SINEs (short interspersed nuclear elements) are a type of much shorter non-LTR retrotransposons.
Non-LTR retrotransposons do not contain long terminal repeats (LTR). However, they contain genes for reverse transcriptase, RNA binding protein, nuclease, and ribonuclease H domain. Non-LTR retrotransposons have short repeats. These repeats have an inverted order of bases next to each other. Apart from that, non-LTR retrotransposons also have direct repeats found in LRT transposons. Non-LTR retrotransposons fall into two categories as LINEs and SINEs.
CONTENTS
1. Overview and Key Difference
2. What are LINEs
3. What are SINEs
4. Similarities – LINEs vs SINEs
5. LINEs vs SINEs in Tabular Form
6. Summary
What are LINEs?
LINEs (long interspersed nuclear elements) are longer non-LTR retrotransposons. They are widespread in the genomes of eukaryotes. They usually make up 21.1% of the human genome. Each LINE is around 7000 base pairs long. LINEs can transcribe into mRNA and translate into a protein that can function as a reverse transcriptase enzyme. This reverse transcriptase produces DNA copies of the LINEs RNA. These DNA copies can be integrated into the genome at a new site.
Figure 01: LINEs and SINEs
The human genome has only one abundant LINE called LINE-1. LINE-1 element is around 6000 base pairs long. There are around 100,000 truncated LINE-1 elements in the human genome. Random mutation can occur in LINEs. Due to random mutations, the LINEs can degenerate. They are no longer transcribed or translated. Furthermore, LINEs are grouped into five main groups such as L1, RTE, R2, I and jockey. These five groups further subdivide into another 28 clades.
LINEs are normally propagated through a mechanism called target primed reverse transcription mechanism (TPRT). Insertion of LINEs causes human diseases like haemophilia A, cancer, mendelian disorders, etc. Hypomethylation of LINEs also triggers certain types of cancer.
What are SINEs?
SINEs (short interspersed nuclear elements) are a type of much shorter non-LTR retrotransposons. They are about 100 to 700 base pairs in length. SINEs are also DNA elements that amplify themselves throughout eukaryotic genomes through RNA intermediates. SINEs make up about 13% of the mammalian genome. The internal regions of SINEs originate from tRNA. It remains highly conserved. They are often present in many species of vertebrates and invertebrates. The copy number variation and mutations in the SINEs can be incorporated to construct the phylogeny-based classification of species.
SINEs can be grouped into three main types: CORE-SINEs, V-SINEs, and AmnSINEs. Alu element is the most common SINE in primates. Moreover, there are more than 50 human diseases associated with the insertion of SINEs. When they insert within or near exons, they can cause improper splicing or change the reading frame. This leads to disease phenotypes such breast cancer, colon cancer, leukaemia, haemophilia, cystic fibrosis, colon cancer, Dent’s disease, neurofibromatosis, etc.
What are the Similarities Between LINEs and SINEs?
- LINEs and SINEsare two types of non-LTR retrotransposons.
- Both do not have long terminal regions (LTR).
- Both are predominantly found only in eukaryotes.
- They are both non-autonomous.
What is the Difference Between LINEs and SINEs?
LINEs are longer non-LTR retrotransposons, while SINEs are much shorter non-LTR retrotransposons. So, this is the key difference between LINEs and SINEs. Furthermore, LINES code for reverse transcriptase enzyme, while SINE does not code for reverse transcriptase enzyme. Thus, this is another difference between LINEs and SINEs.
More differences between LINEs and SINEs are listed below in tabular form for side by side comparison.
Summary – LINEs vs SINEs
Retrotransposons are mainly found in all eukaryotes but absent in prokaryotes. Approximately, 37% of the human genome contains retrotransposons. Retrotransposons are mainly two types: LTR and Non-LTR retrotransposons. Non-LTR retrotransposons do not contain long terminal repeats (LTR), which are present in LTR retrotransposons. Non-LTR retrotransposons are further divided into two categories: LINEs and SINEs. LINEs are longer non-LTR retrotransposons, while SINEs are much shorter non-LTR retrotransposons. Thus, this is the summary of the difference between LINEs and SINEs.
Reference:
1. “Retrotransposon.” An Overview | ScienceDirect Topics.
2. Hancks, Dustin C., and Haig H. Kazazian. “Roles for Retrotransposon Insertions in Human Disease.” Mobile DNA, BioMed Central, 6 May 2016.
Image Courtesy:
1. “LINE1s and SINEs” By Mariuswalter – Own work (CC BY-SA 4.0) via Commons Wikimedia