On principles of organization of polyreplicon systems.

Principles for the acceptability of replicons and polyreplicon systems are formulated, based on the postulated single reproduction of all the components of these systems in each reduplication cycle. On this basis the diverse variants of properties inherent to these systems and their punctuation marks (replicators and terminators) are discussed. The problem of the existence of terminators of reduplication is also considered.Variants of linear polyreplicon systems with identical punctuation are examined. Rules determining the acceptability of different aberrations are put forward. The following variants are unacceptable: inversions the ends of which lie in replicons with the same orientation; non-reciprocal translocations where the ends lie in replicons with opposite orientation; reciprocal translocations of two fragments differing in the orientation of the end replicons; all deletions. It is shown that polyreplicon systems in which all the replicons have the same orientation are subject to maximal losses due to aberrations, whereas systems consisting of two replicon groups equal in total length and having opposite orientation bear minimal losses.The following conclusions are drawn from the comparison of these rules and the analysis of the experimental data: 1)-If terminators exist, replicons of eukaryote chromosomes, in which acceptable aberrations are found, do not overlap and have the same punctuation. 2)- In this case, the alternating orientation of replicons in mammalian chromosomes corresponds to minimal aberrational losses. A hypothesis is proposed for the evolutionary pathway along which linear polyreplicon systems of eukaryotes may have appeared. According to this hypothesis, circular replicons of prokaryotes have united by means of recombination into systems with subsequent selection of variants based on minimal aberrational losses.