Transposons: What Are They? What Do They Do? Do They Do Things? Let's Find Out.
Iâve talked before the research done in my lab here, but I havenât talked about my personal research interests. My of interest is, yes you read the title, transposons. What are transposons though? Transposons, or transposable elements, are bits of genetic code that is transposable (hence the name). In essence, I, you, and nearly every organism that has ever existed has bits of DNA in them that will jump around at random. One minute you could have DNA in spot A in chromosome 1, and the next day it will be in spot Q in chromosome 12. This is the nature of a transposable element.
Transposons were discovered in the late 40s by Barbara Mcclintock while experimenting with maize with broken chromosomes who had noticed that some leaves had unusual color patterns. She hypothesized that these were due to certain parts of the gene breaking in some cells and being added to other cells during cell division. This turned out to be false after she had observed that parts of chromosomes had switched places. The fact that DNA could move was so groundbreaking that she was largely ignored for 20 years. However, her work was fortunately rediscovered when transposable elements were discovered in bacteria in the late 70s. And in 1983 she won a Nobel prize for Physiology or Medicine, so the waiting game did pay off eventually.
Today we know transposable elements are in nearly every organism, from the lowly starfish to the mighty echidna, and everything else with DNA. Why and how they came to exist is anyoneâs guess. Itâs possible that one transposon developed in the first organism and spread, or it occurs multiple times separately. We donât have DNA samples from the dawn of life, which makes answering this question very hard. Another curiosity of the transposon is how similar it operates to a retrovirus. A retrovirus inserts its own DNA to a host cellâs DNA (like a transposon) to trick the host into producing more viruses (also like a transposon).
There are two classes of transposons, aptly named Class I and Class II, and both of these classes has to do with how they âjumpâ. Class I transposons (aka retrotransposons) move by being copied into DNAâs sister molecule, RNA. The RNA, now free from the chromosome, moves around until it is copied back into DNA. Like a bad neighbor, this DNA then takes the liberties of reinserting itself back into the DNA.
Class II transposons (aka DNA transposons) are much more direct. Instead of going through the messy process of being copied and converted multiple times, it just up and leaves the spot in the chromosome itâs located in and then enters a new area. Whatâs good (for the transposons anyway) is that most of the information needed to move is located within the transposon, meaning that as long as it doesnât mutate it can keep up this seemingly random nomadic lifestyle.
But mutations do happen, and the transposon needs a very specific pattern to work, so your genome is littered with transposons that no longer work. In fact, 50% of your DNA is composed of âdeadâ transposons. To keep this in perspective, only 2% of your genome is actually used as a blueprint for your body. Fortunately for you, less than .05% of your genome has active transposons. These active transposons are mostly harmless so you can sleep well tonight, but that doesnât mean they affect evolution, disease, and mutations, which Iâll go over in next weekâs blog.
