There are other methods besides PCR, but PCR was the first method and it was Kary B Mullis who established it really, and got a Nobel Prize for it, although very important work in this field also was done in Gobind Khorana's laboratory. Now the other method... I perhaps should mention another one, which is called the 3SR method. I don't tell the abbreviation but I rather describe the method. You need three enzymes for the method, but that's not the 3SR, it does not refer to three enzymes. But what is it? It's first of all an isothermal method... you don't have to cyclise the temperature. Second, you start with the reverse transcriptase, that's the enzyme of the AIDS virus. That is able to transcribe the RNA back into DNA. You might remember that the dogma of molecular biology is that the information is in DNA, that's in a stable form there, that is transcribed into RNA where it's in a labile form and the RNA informs the protein factories, so that protein comes out of that DNA RNA protein.
But meanwhile one found an enzyme which can re-transcribe the RNA into DNA, and that's a whole class of viruses utilises this enzyme. They are called the retroviruses... utilises this enzyme to infect the cell, re-transcribe their RNA into DNA which then can be incorporated into the genome of the cell, though that's a very diabolic way of establishing the wrong genes in organisms. Yes, using this enzyme means that you start with an RNA molecule, you re-transcribe it into DNA, and then you take another enzyme, which is a so-called T7 polymerase, which means it is taken from a phage T7, and it is the polymerase which copies DNA and makes RNA. So you first re-transcribe the RNA into DNA, and now the polymerase comes and makes about one hundred RNA molecules from that DNA molecule. Now most of that RNA you decompose then by a nuclease, but before you decompose it you re-transcribe your amplified RNA into DNA and again each DNA makes one hundred RNA. You see while in the PCR reaction you make two, four, eight, sixteen, here you make 100 in the first step when the DNA is copied into RNA, in the next step you make 100 x 100, or perhaps a few less than that, and so you have a much steeper increase which for many of our methods turned out to be of advantage.
[Q] And the quality is the same?
Yes. Yes, the quality is... well, it's even easier to handle because you can do all your work at 40°C, whereas the other you have to heat up to nearly the boiling point, to above 90°C. And there are more, even other, amplification methods, I will not go into all the details, but the existence of these amplification methods was important for our evolutionary technology.
