title: A nucleotide composition constraint of genome sequences.
abstract: Let a, c, g and t denote the occurrence frequencies of A, C, G and T, respectively, in a genome. We calculated the statistical quantity S = a2 + c2 + g2 + t2 for each of 809 genomes (11 archaea, 42 bacteria, 3 eukaryota, 90 phages, 36 viroids and 627 viruses) and 236 plasmids. We found that S < 1/3 is strictly valid for almost all of the above genomes or plasmids. As a direct deduction of the above observation, it is shown that (i) the statistical quantity S is a kind of genome order index, which is negatively correlated with the Shannon H function; (ii) S < 1/3 suggests that a minimal value of the Shannon H function is required for each genome; (iii) S defined above would be a new biological statistical quantity, useful to describe the composition features of genomes; (iv) By jointly considering the Chargaff Parity Rule 2, it is shown that the genomic G + C content should be in between 0.211 and 0.789.
authors.affiliation: Department of Physics, Tianjin University, Tianjin 300072, China. ctzhang@tju.edu.cn
authors.forename: Chun-Ting
authors.initials: CT
authors.lastname: Zhang
authors.forename: Ren
authors.initials: R
authors.lastname: Zhang
mesh_terms: D000818:Animals; D001105:Archaea; D001419:Bacteria; D001482:Base Composition; D004247:DNA / Q000145:classification / Q000235:genetics; D005057:Eukaryotic Cells; D005658:Fungi; D016678:Genome; D006801:Humans; D009711:Nucleotides / Q000737:chemistry / Q000235:genetics*; D010957:Plasmids / Q000235:genetics; D017421:Sequence Analysis; D013223:Statistics as Topic; D014780:Viruses
chemical_list: D009711:Nucleotides; D004247:DNA