The set of all sequences that are generated by a biomolecular protocol forms a language over the four letter alphabet Δ={A,G,C,T}. This alphabet is associated with a natural involution mapping θ, A↦ T and G↦ C which is an antimorphism of Δ*. In order to avoid undesirable Watson-Crick bonds between the words (undesirable hybridization), the language has to satisfy certain coding properties. In this paper we build upon the study initiated in [11] and give necessary and sufficient conditions for a finite set of “good” code words to generate (through concatenation) an infinite set of “good” code words with the same properties. General methods for obtaining sets of “good” code words are described. Also we define properties of a splicing system such that the language generated by the system preserves the desired properties of code words.

Languages of DNA Based Code Words

On properties of bond-free DNA languages

We formalize the notion of a DNA hairpin secondary structure, examining its mathematical properties. Two related secondary structures are also investigated, taking into the account imperfect bonds (bulges, mismatches) and multiple hairpins. We characterize maximal sets of hairpin-forming DNA sequences, as well as hairpin-free ones. We study their algebraic properties and their computational complexity. Related polynomial-time algorithms deciding hairpin-freedom of regular sets are presented. Finally, effective methods for design of long hairpin-free DNA words are given.

Hairpin structures in DNA words

For an involution ? : ?* ? ?* over a finite alphabet ? we consider involution codes: ?-infix, ?-comma-free, ?-k -codes and ?-subword-k-codes. These codes arise from questions on DNA strand design. We investigate conditions under which both X and X+ are same type of involution codes. General methods for generating such involution codes are given. The information capacity of these codes show to be optimized in most cases. A specific set of these codes was chosen for experimental testing and the results of these experiments are presented.

Involution codes: with application to DNA coded languages

The paper examines the concept of hairpin-free words motivated from the biocomputing and bioinformatics fields. Hairpin (-free) DNA structures have numerous applications to DNA computing and molecular genetics in general. A word is called hairpin-free if it cannot be written in the form xvyθ (v)z, with certain additional conditions, for an involution θ (a function θ with the property that θ2 equals the identity function).

We consider three involutions relevant to DNA computing: a) the mirror image function, b) the DNA complementarity function over the DNA alphabet {A,C,G,T} which associates A with T and C with G, and c) the Watson-Crick involution which is the composition of the previous two. We study elementary properties and finiteness of hairpin (-free) languages w.r.t. the involutions a) and c). Maximal length of hairpin-free words is also examined. Finally, descriptional complexity of maximal hairpin-free languages is determined.

David Kephart

Papers

Generating DNA Code Words.