A pentapeptide-based method for protein secondary structure prediction.

We present a new method for protein secondary structure prediction, based on the recognition of well-defined pentapeptides, in a large databank. Using a databank of 635 protein chains, we obtained a success rate of 68.6%. We show that progress is achieved when the databank is enlarged, when the 20 amino acids are adequately grouped in 10 sets and when more pentapeptides are attributed one of the defined conformations, alpha-helices or beta-strands. The analysis of the model indicates that the essential variable is the number of pentapeptides of well-defined structure in the database. Our model is simple, does not rely on arbitrary parameters and allows the analysis in detail of the results of each chosen hypothesis.

Fast DNA sequencing.

A method for fast nucleotide sequencing is described. It is based in the selection of well-known small oligomers able to be hybridized with the unknown target. The selected oligomers are afterwards ordered following a simple statistical approach. The use of capillary electrophoresis for the analysis is emphasized.

Biocryptography.

A new cryptology that uses biomolecules as carriers of hidden information is described here. The huge dimension of biopolymers permits the insertion there of private messages and the rapidity and specificity of biomolecular interactions facilitate the identification of classified communications. Otherwise, this process can be implemented in a virtual context.

Secondary structure of proteins and three-dimensional pattern recognition.

We describe a new, parameter-free, method to predict the secondary structure of a protein. It is based on the recognition of well-defined pentapeptides, which allows the discrimination of alpha helices, beta sheets and random coils in proteins. Presently, a success rate of about 65% is achieved for a three-state model.

Can biological homochirality result from a phase transition?

The problem of chiral purity in living organisms is still one of the prominent difficulties in the study of the origins of life. In particular the parity non-conservation known to occur in weak interactions could not be related to this lack of symmetry: these physical forces, though universal, are very weak and up to now no amplification process had been proposed. In 1991, A. Salam remarked that, due to the attractive character of the parity violating force in electro-weak interactions, a phase transition at low temperature should exist, leading eventually to enantiomeric purity. We undertook then a series of experimental tests, looking for a sizeable change in the optical activity of cystine molecules. We found no evidence for the phase transition down to 0.01 K. The interpretation of these negative results will be discussed, and future experiments proposed.

Optimization and the genetic code.

The present paper will focus on the relation between the structure of the table of the genetic code and the evolution of primitive organisms: it will be shown that the organization of the code table according to an optimization principle based on the notion of resistance to errors can provide a criterium for selection. The ordered aspect of the genetic code table makes this result a plausible starting point for studies of the origin and evolution of the genetic code: these could include, besides a more refined optimization principle at the logical level, some effects more directly related to the physico-chemical context, and the construction of realistic models incorporating both aspects.

Information theory and the genetic code.

The genetic code, which directs the protein biosynthesis, is an information system. Although all its details are not known at present, its essential characteristics are elucidated, as well for the replication or transcription as for the translation of the genetic message. A coherent picture now appears, which reveals the existence of an universal structure, the most fundamental features of which seem to obey some logic. A systematic approach has been devised, which aims to their integration in a theorectical scheme: many features of the code table can thus be interpreted as resulting from a unique principle of best resistance against the effects of mutations. Any group of triplets or amino-acids can be considered along this line. It is more difficult however, to analyse the coexistence of two (or more) different groups. In this work, we propose to extend our optimization principle into a more general one, which includes the notion of information as defined by Shannon. We explore some consequences of this new principle in the most simple models that one can build for the origin and evolution of the genetic code.

Genetic code and optimal resistance to the effects of mutations.

This paper deals with the notion of resistance of the genetic code to the effects of mutations. We measure the resistance of a group of t codons as the number of pairs of those which differ from each other in only one of their three bases. We find for each value of t the maximum possible value of the resistance and we describe some groups of codons giving this value. Important examples of such configurations are found in the genetic code, among these are the groups of synonymous codons, as observed elsewhere, and the cluster of codons which have an hydrophobic amino acid for translation.

The logic of the genetic code: synonyms and optimality against effects of mutations.

The groups of codons which correspond to the same amino-acid in the genetic code (synonyms) are compared to theoretical codes constructed so as to resist best to the effects of mutations. The analysis shows that the genetic code presents synonymy structures which are optimized against translation errors.

[Origin and evolution of the genetic code]. / L'origine et l'évolution du code génétique.

We propose a quantitative model which suggests that the present genetic code appeared under the influence of mutations, while optimizing its own resistance against their effects. Its evolution was realized by successive steps in which the number of translated codons grew, whereas the number of terminators decreased. The main constraint of this model is selection against nonsense mutations: the competition among many primitive codes gives advantage to those which resist best to the occurrence of nonsense mutations. The structures of the selected systems converge towards that of the present genetic code. This one appears then as built so as to resist to errors, information noise, mutations.