[Possible function and origin of crossing over].

Abstract

Crossing over to repair genetic material via exchange probably emerged at the initial stages of organic evolution, earlier than the appearance of the DNA molecule in its present form. In that period, nitrous bases existed as free molecules, although, like in double-helical DNA, they formed aggregates. The electrochemical characteristics of pyrimidines differ from one another to a greater extent than those of purines, which are almost electrically neutral. Therefore, it is possible that the DNA electrostatic balance is accounted for by nonspecific interaction between pyrimidine bases. The data obtained by Nussinov et al. indicate that, in homooligomers, the arrangement of pyrimidine bases in opposite DNA strands exhibits some restrictions with respect to their mutual positions. In functioning DNA, the electrostatic balance of pyrimidine arrangement in complementary strands may favor rapid transitions of the molecule between an open helix and the original state. It is supposed that crossing over restores the electrostatically balanced spatial arrangement of pyrimidine homooligomers and, hence, the functional activity of the entire DNA molecule.