What Is a Transposable Element?

Transposable factors (also called movable, movable factors) are a type of mobile genetic factors found in many post-animals, including nematodes, insects, and humans. A piece of DNA sequence can be copied or broken separately from in situ, inserted into another site after circularization, and regulates the genes behind it. This process is called transposition. This sequence is called the jumping gene or transposon insertion sequence (Is factor), transposition (Tn), and transposition phage. Transposons are the basic units that exist on the chromosomal DNA and can autonomously replicate and shift. The simplest transposons are called insert sequences (IS) because they do not contain any host genes. They are normal parts of bacterial chromosomes or plasmid DNA. A transposon is a movable DNA sequence in the genome. It can "jump" from one position to another in the genome through a series of processes such as cutting and reintegration.

Prior to the 1950s, people generally understood that the amount of DNA in each genome was fixed, which included a series of genes with a fixed number, a fixed position, and a fixed function to keep biological traits inherited stably. But at the same time, genes also mutate. Generally, the frequency of spontaneous mutation is very low, and of course there is a phenomenon of high mutation frequency, which indicates that there are highly unstable genes in the genome, which has been ignored for a long time. . The first person to notice the unstable genes was De. Vires, who studied the unstable mutation of the color of snapdragon flowers at the end of the 19th century, but failed to make a theoretical explanation. In the first few decades of this century, RAEmesor studied mutant lines of maize that can interfere with the orange-red pigment synthesis in the seed coat. He proposed that back mutations occur during grain development, and that the streaks of colored cells and colorless cells are formed by unstable The recessive gene was caused, but he did not know what caused the recessive city to be unstable. Although McClintock discovered transposable elements in corn as early as 1951, it was difficult to accept the new concept of "jumping genes" because of the traditional idea that genes are arranged in order on chromosomes, so it was not until 1967 that Shapiro Only found transposable elements in E.coli . He found a polar mutation in the galactose operon. The gal operon has three genes: gal K, T, and E. They encode three enzymes that catalyze the catabolism of Gal. Its intermediate product Gal-1-p is toxic, so galT- is difficult to survive due to the accumulation of Gal-1-p on the medium containing half sugar. Then the various mutants that can grow on this medium should be the back mutations of galt- and galK -galT- (because it cannot produce Gal-1-p), but it was unexpectedly found that galE-galT- can also survive It is reasonable to say that this mutant type makes Gal-1-p accumulation impossible to survive, but actually grows well. What is the reason for this? Further research revealed that galE- is a polar mutation, and because of its mutation, the activity of galK far from the manipulation site is greatly reduced, so Gal-1-p will not accumulate in the cell, and the transposable factor was isolated for the first time. The physical characteristics of the transposable factor have confirmed the correctness of the transposable factor theory. So far, transposable elements have been isolated from several prokaryotic and eukaryotic organisms, and the DNA level is being studied ^[1]

Since 1928, F. Criiffith's experiment with Pneumococcus infection on Mus musculus, it was found out that the transformation factor that caused the transformation from R strain to S strain was DNA, and it was not until 1943 that the spontaneous mutation of the bacteria was determined. Nature. A large number of experiments in the future have shown that the conduction phenomenon of transfer in bacteria is due to the presence of a mobile factor in the bacteria-transposable factors. The following summarizes the results of studies on the types and genetic effects of transposition factors of prokaryotes ^[1]

In 1947, McClintock, the "Madam Corn" of Cold Spring Harbor Laboratory in the United States, first discovered and described the transposition factor in corn. The discovery of transposable elements has broken the traditional concept of genetics about the fixed arrangement of genes on chromosomes and the exchange of homologous chromosomes, and has revealed the fluidity of genes, which is of great significance ^[3]

There is no doubt that the study of transposable factors has become one of the hot spots of theoretical and experimental biological research. There are two main reasons for this: First, the establishment of the theory of transposition has gone through twists and turns, was discovered in the 1930s, formed the theory in the 1940s, and was accepted by the scientific community in the 1980s, which contained rich scientific ideas and philosophy of life; The study of transposable factors is of great significance for basic research and applied research in biological evolution, species formation, cell differentiation, gene cloning, transgenic technology, and molecular biology, molecular genetics, genetic engineering, population genetics, etc. ^[4] .