title: A-T rich sequences in vertebrate DNA. A possible explanation of q-banding in metaphase chromosomes.
abstract: Partially denatured DNAs from mouse, cow, and chicken were visualized in the electron microscope by the basic protein film technique and the size and distribution of the denatured regions characterized. A-T rich sequences visualized at 15% denaturation average about 1500 bases in length for all three species and are arranged quite non-randomly in the genome. This arrangement is such that 30--50% of the entire genome contains no A-T rich DNA, and another 20% is composed about one-half of A-T rich sequences and one-half of other sequences. Comparison with DNA denaturation profiles indicates that for each organism these sequences are from 25--30% G+C and that there is very little if any DNA more A-T rich than these. Estimates from published studies of fluorescence enhancement of quinacrine bound to A-T rich DNAs suggest that the observed non-random organization of A-T rich sequences is sufficient to account for Q banding of metaphase chromosomes.
mesh_terms: D000225:Adenine / Q000032:analysis*; D000818:Animals; D002417:Cattle; D002645:Chickens; D002871:Chromosome Banding; D002875:Chromosomes / Q000032:analysis*; D003596:Cytosine / Q000032:analysis; D004247:DNA / Q000032:analysis*; D006147:Guanine / Q000032:analysis; D051379:Mice; D008854:Microscopy, Electron; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D013941:Thymine / Q000032:analysis*
chemical_list: D006147:Guanine; D003596:Cytosine; D004247:DNA; D000225:Adenine; D013941:Thymine