The Standard Genetic Code can Evolve from a Two-Letter GC Code Without Information Loss or Costly Reassignments

On the context-sensitive grammar of the genetic code

We address the possibilities of the semiotic description of the genetic information as a dual and self-replicative system of correspondence between its biochemical substance and semiotic form of organization. Combining the principles of contextual dependence and arbitrariness of sign leads to the conclusion that the genetic code's primary elements (nucleotides) can be considered not as biochemical constants but as semiotic or, more precisely, grammatical variables. We suggest describing the genetic code as a language, consisting of 1) units of the alphabet; 2) a vocabulary that includes meaningful items and the rules of correspondence between units of different levels; 3) context-sensitive grammar - a system of rules for the formation of units based on abstract grammatical categories.

From Matter to Form: the Evolution of the Genetic Code as Semio-Poiesis

The code is meaningless unless translated. (Monod 1971, 143)

We address issues of a description of the origin and evolution of the genetic code from the semiotics standpoint. Developing the concept of codepoiesis introduced by M. Barbieri, a new idea of semio-poiesis is proposed. Semio-poiesis, a recursive auto-referential processing of a semiotic system, becomes a form of organization of the bio-world when and while notions of meaning and aiming are introduced into it. The description of the genetic code as a semiotic system (grammar and vocabulary) allows us to apply the method of internal reconstruction to it: on the basis of heterogeneity and irregularity of the current state, to explicate possible previous states and various ways of forming coding and textualization mechanisms. The revealed patterns and irregularities are consistent with hypotheses about the origin and evolution of the genetic code.

Mixed circular codes

By an extensive statistical analysis in genes of bacteria, archaea, eukaryotes, plasmids and viruses, a maximal C³-self-complementary trinucleotide circular code has been found to have the highest average occurrence in the reading frame of the ribosome during translation. Circular codes may play an important role in maintaining the correct reading frame. On the other hand, as several evolutionary theories propose primeval codes based on dinucleotides, trinucleotides and tetranucleotides, mixed circular codes were investigated. By using a graph-theoretical approach of circular codes recently developed, we study mixed circular codes, which are the union of a dinucleotide circular code, a trinucleotide circular code and a tetranucleotide circular code. Maximal mixed circular codes of (di,tri)-nucleotides, (tri,tetra)-nucleotides and (di,tri,tetra)-nucleotides are constructed, respectively. In particular, we show that any maximal dinucleotide circular code of size 6 can be embedded into a maximal mixed (di,tri)-nucleotide circular code such that its trinucleotide component is a maximal C³-comma-free code. The growth function of self-complementary mixed circular codes of dinucleotides and trinucleotides is given. Self-complementary mixed circular codes could have been involved in primitive genetic processes.