title: New alphabet-dependent morphological transition in random RNA alignment.
abstract: We study the fraction f of nucleotides involved in the formation of a cactuslike secondary structure of random heteropolymer RNA-like molecules. In the low-temperature limit, we study this fraction as a function of the number c of different nucleotide species. We show, that with changing c, the secondary structures of random RNAs undergo a morphological transition: f(c)→1 for c≤c(cr) as the chain length n goes to infinity, signaling the formation of a virtually perfect gapless secondary structure; while f(c)<1 for c>c(cr), which means that a nonperfect structure with gaps is formed. The strict upper and lower bounds 2≤c(cr)≤4 are proven, and the numerical evidence for c(cr) is presented. The relevance of the transition from the evolutional point of view is discussed.
authors.affiliation: Moscow Institute of Physics and Technology, 141700, Dolgoprudny, Russia.
authors.forename: O V
authors.initials: OV
authors.lastname: Valba
authors.forename: M V
authors.initials: MV
authors.lastname: Tamm
authors.forename: S K
authors.initials: SK
authors.lastname: Nechaev
mesh_terms: D008957:Models, Genetic; D009690:Nucleic Acid Conformation; D012313:RNA / Q000737:chemistry* / Q000235:genetics*
chemical_list: D012313:RNA