DNA of ciliated protozoa: DNA sequence diminution during macronuclear development of oxytricha

We have measured the reassociation kinetics of DNA from the micronucleus and from the macronucleus of the hypotrichous cillate 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 × 10¹¹ daltons; the haploid DNA content of the micronucleus is 4 × 10¹¹ 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 × 10¹⁰ 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 pleces with an average molecular weight of 2.1 × 10⁶ daltons. Since the kinetic complexity of macronuclear DNA is 3.6 × 10¹⁰ daltons, the macronucleus must contain about 17,000 different kinds of DNA pieces.Each macronucleus contains 3.5 × 10¹³ daltons (58 pg) of DNA, indicating that each sequence must be present about 1000 times per macronucleus or 2000 times per cell.