title: The frequency of two-base tracts in eukaryotic genomes.
abstract: The frequency of two-base tracts is surveyed in a wide range of eukaryotic genomes using the special program TRACTS. All three two-base families are surveyed: R.Y (A,G.C,T), K.M (A,C.G,T), and S;W (A.T and G.C). Data for the human beta-globin complex, for the tobacco chloroplast, and for 247 nt mammalian promoter regions are presented. All two-base tracts longer than three or four bases are overrepresented to an extent surpassing by far their occurrence in a randomized DNA population in the majority of the genomic regions analyzed; 20-30 long tracts are quite frequent, against the statistical odds. R.Y tracts are found at the largest excess, K.M tract to a slightly lesser extent, while S.W tracts are found at a moderate yet significant excess. The majority of the tracts manifest only a limited extent of tandem repeat structures. The idea that the two base tracts serve as unwinding elements is considered.
authors.affiliation: Department of Cell Biology, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: G
authors.initials: G
authors.lastname: Yagil
mesh_terms: D000818:Animals; D001482:Base Composition; D001483:Base Sequence; D004247:DNA / Q000737:chemistry / Q000235:genetics*; D016678:Genome; D005914:Globins / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D010947:Plants, Toxic; D011401:Promoter Regions, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D014026:Nicotiana / Q000235:genetics
chemical_list: D005914:Globins; D004247:DNA