Sunday, March 5, 2017

Introns explained with the Organelle Escape Theory

I have always been very interested in finding out how things work, and life is the most interesting. A part of understanding how things work is to understand WHY it was built that way, how the designer was thinking when he decided that solution. For life there is no designer, instead understanding evolution is of the greatest interest. A part of understanding evolution is to understand how the cells have evolved, especially the relation between eukaryotes and bacteria. Two important discoveries that were both made in 1977:

  1. It was found that there are two distinct types of bacteria
  2. It was also found that most of our DNA is not expressed, specially that there are long sequences called introns in our genes that are spliced out before the genes are used to produce proteins
This was about the same time that Margulis’ endosymbiosis theory was accepted. I was speculating during the 1980es how all these discoveries could work together, and it was especially the finding of introns exclusively in the nucleus of eukaryotes, not in any bacteria and not in any of the eukaryotic organelles, that was an enigma. But I was convinced that this was a crucial fact to use in the search for the solution.

It occurred to me in 1994, while reading an article by Leslie Orgel, that eukaryotes are a better candidate for the original organism than the bacteria. They have much more relics from the RNA world, and they are still using them actively. One example is the spliceosomes, that splice the introns, another is the ribosomes, that are used to translate mRNA to proteins. They are used also in bacteria, so I figured that the eukaryotes could somehow have filtered out what was most essential and given this to the bacteria. There is one natural process that removes introns. That is the splicing process that takes place in the eukaryotic cytosol. If the first organelles were produced in their host, than they would naturally use mRNA from the cytosol. A DNA chromosome could easily be produced by reverse transcription from mRNA and a linking process. If bacteria are based on organelles, then they would naturally have no introns. We can say that the organelles worked as a filter that removed all spliceosomal introns, also for their descendants, the bacteria.

There are two conflicting theories for intron evolution, introns-early and introns-late. The former is the most logical. The latter is more or less a construction to match with bacteria-early. It assumes that spliceosomal introns can be created. But there is no known way that could happen. Introns type II can be inserted, but they are of another kind. With OET the most logical solution can be chosen.

I was convinced that the Organelle Escape Theory was the right explanation already in 1994, and I have become more and more convinced since then. One example of an article that supports the theory that eukaryotes are older than the bacteria is one by Anthony Poole, Daniel Jeffares, and David Penny: Early evolution: the new kids on the block. Other observations that support my theory are the findings of organelles like hydrogenosomes and mitosomes. They are in conflict with the endosymbiosis theory.

With my theory eukaryotes would have very long time for evolution of the eukaryotic complexity. Introns serve as delimiters that define genetic building block. They have helped this evolution. 

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