title: CpG deficiency, dinucleotide distributions and nucleosome positioning.
abstract: The dinucleotide CpG is deficient in (A + T)-rich regions of vertebrate DNA in both coding and non-coding sequences and there is a corresponding increase above expectation in the occurrence of TpG and CpA. By contrast in (G + C)-rich regions no deficiency of CpG is found. Such (G + C)-rich sequences, containing the expected number of CpG dinucleotides, alternate along the genome with (A + T)-rich sequences which have a lower than expected CpG content. The G + C content of vertebrate DNA can oscillate with a period of 150-200 bp and this may be a factor in positioning nucleosomes. The role of mutagenesis in loss of CpG and increase of A + T, particularly in non-coding regions, is discussed.
mesh_terms: D001482:Base Composition; D001483:Base Sequence; D003568:Cytidine Monophosphate / Q000031:analogs & derivatives; D003597:Cytosine Nucleotides; D004247:DNA / Q000235:genetics*; D015226:Dinucleoside Phosphates; D005796:Genes; D006151:Guanosine / Q000031:analogs & derivatives*; D009707:Nucleosomes / Q000648:ultrastructure*; D012984:Software
chemical_list: D003568:Cytidine Monophosphate; D003597:Cytosine Nucleotides; D004247:DNA; D015226:Dinucleoside Phosphates; D006151:Guanosine; D009707:Nucleosomes; C015772:CpG dinucleotide