title: DNA of ciliated protozoa: DNA sequence diminution during macronuclear development of Oxytricha.
abstract: We have measured the reassociation kinetics of DNA from the micronucleus and from the macronucleus of the hypotrichous ciliate Oxytricha. The micronuclear DNA reassociates with at least a two-component reaction, indicating the presence of both repeated and non-repeated sequences. The kinetic complexity of micronuclear non-repeated DNA is in the range of 2 to 15 X 10(11) daltons; the haploid DNA content of the micronucleus is 4 X 10(11) daltons (0.66 pg), measured microspectrophotometrically. The DNA of the macronucleus reassociates as a single second-order reaction, with a kinetic complexity of 3.6 X 10(10) daltons. A comparison of the kinetic complexities of micronuclear and macronuclear DNAs suggest a 5 to 30 fold reduction in DNA sequence complexity during the formation of a macronucleus from a micronucleus. Macronuclear DNA is in pieces with an average molecular weight of 2.1 X 10(6) daltons. Since the kinetic complexity of macronuclear DNA is 3.6 X 10(10) daltons, the macronucleus must contain about 17,000 different kinds of DNA pieces. Each macronucleus contains 3.5 X 10(13) daltons (58 pg) of DNA, indicating that each sequence must be present about 1000 times per macronucleus or 2000 times per cell.
mesh_terms: D000818:Animals; D001483:Base Sequence; D002455:Cell Division; D002467:Cell Nucleus / Q000032:analysis*; D016798:Ciliophora / Q000032:analysis* / Q000254:growth & development; D003596:Cytosine / Q000032:analysis; D004247:DNA / Q000032:analysis*; D006147:Guanine / Q000032:analysis; D009691:Nucleic Acid Denaturation; D009695:Nucleic Acid Renaturation
chemical_list: D006147:Guanine; D003596:Cytosine; D004247:DNA