DNA amounts in the nuclei ofParamecium aurelia andTetrahymena pyriformis

Abstract

Abstract. DNA amounts have been determined in the micronuclei and macronuclei of 8 strains of Paramecium aurelia and 6 strains of Tetrahymena pyri/ormis.

Interstitial telomeres are hotspots for illegitimate recombination with DNA molecules injected into the macronucleus of Paramecium primaurelia.

“…The exact number of macronuclear chromosomes is hard to assess because of the multiple levels of heterogeneity of chromosome ends (Baroin et al, 1987;Forney and Blackburn, 1988;Caron and Meyer, 1989), and the different estimations of the complexity of the haploid genome (Gibson and Martin, 1971;Cummings, 1975;MacTavish and Sommerville, 1980). Nevetheless, the average size of the macronuclear chromosomes being -300 kb (Preer and Preer, 1979;Caron and Meyer, 1989), an estimation of 300-1000 haploid chromosomes per macronucleus would be fairly accurate.…”

“…No conserved or repetitive sequence elements other than the ones discussed below were observed. Paramecium macronuclear DNA is adenine-and thymine-rich (AT-rich; Gibson and Martin, 1971;MacTavish and Sommerville, 1980;Soldo et al, 1981) and all insertion sites were in AT-rich sequences, without any significant open reading frames. Likewise, no duplication of even short repeats could be detected at the 5' and 3' insertion boundaries for any clone; Insertion frequently occurs in or near internal telomeric repeats A striking feature revealed by the junction sequences was the presence of telomeric repeats next to two insertion junctions (Inl and In7; see Figure 3b).…”

Induction of specific macronuclear developmental mutations by microinjection of a cloned telomeric gene in Paramecium primaurelia.

“…These processes occur to various extents in different species of ciliates (for review, see Yao 1989). In Paramecium primaurelia, reduction of chromosome size obviously occurs during macronuclear development, because the size of macronuclear chromosomes ranges from 50 to 800 kb (Caron and Meyer 1989), with an average of about 300 kb (Freer and Freer 1979), whereas the 30 to 60 micronuclear chromosome pairs (Sonneborn 1974), representing a haploid genome which has been variously estimated to contain between 45,000 and 280,000 kb (Gibson and Martin 1971;Cummings 1975;McTavish and Sommerville 1980), should be much longer on average. Because there appears to be little or no reduction in genome size during macronuclear development (Allen and Gibson 1972;McTavish and Sommerville 1980), chromosome breakage is very likely to occur, leading to the formation of new telomeres in the macronucleus.…”

[6N]METHYL ADENINE IN THE NUCLEAR DNA OF A EUCARYOTE, TETRAHYMENA PYRIFORMIS

“…level (26)(27)(28), uhrastructure (29)(30)(31), ability to synthesize R N A (32)(33)(34), time in the cell cycle at which they synthesize D N A (27,35,36), and in the time and manner in which they divide (30,37). Finally, during conjugation the macronucleus breaks down, and the micronucleus undergoes meiosis and fertilization, giving rise to a new line of both macro-and micronuclei.…”