A new method to find a set of energetically optimal RNA secondary structures

A hypercycle theory of proliferation of viruses and resistance to the viruses of transgenic plant

A set of dynamical equations for the proliferation of two typical viruses TMV and PVY has been derived from the reaction equations describing their replication, assembly and translation. These equations can be seen as the generalization of hypercycle theory to the system. The quantitative explanation on the phenomena of proliferation of plant virus and the mechanism of resistance to the disease of transgenic plant is offered. The phenomenon of specific cessation of minus-strand RNA accumulation in the proliferation of TMV, the cross-protection of plant viruses and the mechanism of resistance to viruses of transgenic plant are discussed based on the computer simulation of the proliferation of viruses and the prediction of the secondary structure of the genomic RNA.

A genetic algorithm to search for optimal and suboptimal RNA secondary structures

Genetic algorithms are a search method used in solving problems by selection, recombination and mutation of tentative solutions, until the better ones are achieved. They are very efficient when the 'building block' hypothesis is effective for the solutions, which means that a better solution can be obtained by assembling short 'motifs' or 'schemata' that can be retrieved in some other worse solutions. The additive nature of the secondary structure free energy rules suggests the validity of this hypothesis, and therefore the likely power of a genetic algorithm approach to search for RNA secondary structures. We describe in detail an original genetic algorithm specific for this problem. The sharing function used to obtain differentiated solutions is also described. It results in a greater effectiveness of the algorithm in retrieving a large number of suboptimal RNA foldings besides the optimal one. RNA sequences of different length are used to test the method. The PSTV viroid sequence has been studied.

Recognition of the folding consensus in RNA secondary structures by the topological-filtering method

Functionally homologous RNA sequences can substantially diverge in their primary sequences but it can be reasonably assumed that they are related in their higher-degree structures. The problem to find such structures and simultaneously satisfy as far as possible the free-energy-minimization criterion, is considered here in two aspects. Firstly a quantitative measure of the folding consensus among secondary structures is defined, translating each structure into a linear representation and using the correlation theorem to compare them. Secondly an algorithm for the parallel search for secondary structures according to the free-energy-minimization criterion, but with a filtering action on the basis of the folding consensus measure is presented. The method is tested on groups of RNA sequences different in origin and in functions, for which proposals of homologous secondary structures based on experimental data exist. A comparison of the results with a blank consisting of a search on the basis of the free energy minimization alone is always performed. In these tests the method shows its ability in obtaining, from different sequences, secondary structures characterized by a high-folding consensus measure also when lower free energy but not homologous structures are possible. Two applications are also shown. The first demonstrates the transfer of experimental data available for one sequence, to a functionally related and therefore homologous one. The second application is the possibility of using a topological probe in the search for precise structural motifs.

Three-dimensional folding of Tetrahymena thermophila rRNA IVS sequence: a proposal

We studied the Tetrahymena thermophila rRNA IVS sequence with the aim of obtaining a model of the structure characterized by the bases proximity of the self-reactions sites. The considered sequence kept up those fragments essential for its catalytic activity as demonstrated by deletion mutants. The first step was the theoretical analysis with a computer method previously proposed, to find optimal free energy secondary structures with the required features, under the suitable constrains. Then we tried folding the obtained secondary structures, in low resolution tertiary models, which kept up the proximity of the catalytic sites also in the space. The proposed tertiary folding seems to provide for a better explanation to the transesterification mechanisms and moreover it is in good agreement with the experimental data (activity of mutants, enzymatic cleavages, phylogenetically conserved regions).

Secondary structures of Tetrahymena thermophila rRNA IVS sequence involved in its self-splicing reactions: a new computer analysis

The secondary structures of Tetrahymena thermophila rRNA IVS sequence involved in the self-splicing reactions, are theoretically investigated with a refined computer method previously proposed, able to select a set of the deepest free energy RNA secondary structures under constraints of model hypotheses and experimental evidences. The secondary structures obtained are characterized by the close proximity of self-reactions sites and account for double mutations experiments, and differential digestion data.