Four-stranded DNA defies any experimental approach
For the second half of the Symposium on structures of DNA, I felt 'the loneliness in the crowd'. I was struggling inside to figure out what would be the best thing to do next. If I were ever to speak up about the 'Four-stranded DNA' and claim for the Nobel Prize, I would be better come up with descent experimental evidences. But it was hopeless. These unusual conformations of mtDNA was rather scarce and not of the uniform sizes and shapes. It would be impossible to isolate the 'stem-and-loop' molecule in quantity. As soon as I attempt to purify the 'four-stranded' stem portion it would disintegrate. If you ever to talk about DNA structure, or any biological structure in
general, you should use the language of X-ray crystallography or NMR. However, there is no way to obtain a homogeneous solution of the 'stem' DNA, not to mention even growing any crystal out of it. Do I even know the name and function of the mtDNA molecule or gene? No, there is no single soul in the whole world working on pearl millet mtDNA, and I just started looking into it. And it is not as easy as maize mtDNA either.
What if I talk to people working on the model organisms such as phage lambda, E. coli, yeast, fruit fly, and maize? They already have transposable elements to test it on. No, they would not listen to me who comes out of nowhere. If it were that simple and easy they could have finished the story in a couple of months even before I begin figuring out what experiments I should be doing. During coffee breaks those 'established' scientists from 'Big Labs' formed lines on the pay phones calling back the home laboratory. They seemed to be yelling and screaming. "So, did you get the result yet? Good, I will be talking in the next session." "You better hurry up and do the test right away. So and so talked about that and it is all hot here."
It was hopeless. Making a story of four-stranded DNA based merely on an EM picture of stem-and-loop shapes of DNA was only a day dream. It was not a science. I had better give it up. On the other hand, it was too neat an idea to simply dump into a garbage can. Transposable elements were hot topics then. Every one was proposing his own model about the molecular mechanism about how transposable elements jump around and insert onto a new target site. Movable genetic elements all had common features of terminal inverted repeats. Upon transposition to a new site they caused a duplication of 4-9 base pair target sequence in direct orientation. It was generally understood then that an enzyme called transposase would recognize the terminal repeats, and facilitates transposition of the 'jumping gene' into a target site. The idea that terminal inverted repeats could physically make direct contacts in the major groove and recognize each other's repeat as complementary sequences was totally out of sight. Instead, cruciform structure was one of the favorite configurations to explain the utility of inverted repeats.
Double helical structure of DNA has been fixed in everyone's mind as a fact. It had been proven and worked fine as evidenced by the explosive development of molecular biology and genetic engineering. Even with the EM pictures of tight stem-and-loop DNA on hand it took me two whole years before it slowly dawned on me that the stem region might contain a four-stranded DNA.
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