Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

This hypothesis assumes that the presence of introns is connected with the presence of histones in the nucleus of the eukaryotic cells (Csordas 1989).While DNA does not form a very ordered structure in a prokaryotic cell and is thus more or less freely accessible to regulation proteins controlling expression of the individual genes, DNA in the nucleus of a eukaryotic cell is tightly wound around the nucleosomes, frequently formed by basic proteins, histones.Consequently, certain DNA sections are inaccessible for regulation proteins at regular intervals (Lee et al. 1993).Introns can act to shift the regulation area of the individual genes so that their position on the nucleosomes permits interaction with the regulation proteins (Fig. XI.8).According to a different hypothesis, introns balance the content of GC pairs in the DNA so that the DNA has sufficient affinity for histones.

Fig. XI.8 Positioning of regulation areas of genes by insertion of introns. In a eukaryotic cell, the DNA is wound around histones and, together with them, forms another complicated higher-order structure (a). It is possible that the insertion of introns (light sections) of suitable length into suitable positions in the genes shifts the position of the regulation areas of the genes (black sections) to places where they are more readily accessible for regulation molecules, for example to the sections between the individual histones (b).