title: Circular DNA and rolling circles in nucleolar rDNA from mitotic nuclei of Physarum polycephalum.
abstract: 1. About 15% of nucleolar DNA (1.712 g/cm3) from Physarum polycephalum displaying maximum hybridization to ribosomal RNA, is composed of circular DNA of 3.9 +/- 0.2 mum contour length or multiples thereof. 2. A portion of these circular molecules (25%) contained linear DNA pieces longer than circumference length. In a small fraction of circular DNA linear pieces, shorter than the unit length, were observed. 3. Most nucleolar DNA, [3H]thymidine-labeled or hybridizable to ribosomal RNA was separable from chromosomal DNA during G2 phase, mitosis and S phase of the cell cycle. 4. Ribosomal DNA content was not amplified during the cell cycle, was unchanged during exponential or stationary growth phase and amounted to about 0.11 -- 0.21% of nuclear DNA in diploid and hexaploid strains of Physarum or 100--200 ribosomal genes per diploid genome.
mesh_terms: D002455:Cell Division; D002466:Cell Nucleolus / Q000032:analysis* / Q000378:metabolism / Q000648:ultrastructure; D002467:Cell Nucleus / Q000032:analysis*; D004270:DNA, Circular / Q000032:analysis* / Q000378:metabolism; D008938:Mitosis; D008970:Molecular Weight; D009235:Myxomycetes / Q000032:analysis*; D009693:Nucleic Acid Hybridization; D010804:Physarum / Q000032:analysis* / Q000378:metabolism; D012335:RNA, Ribosomal / Q000096:biosynthesis; D012270:Ribosomes / Q000032:analysis; D014158:Transcription, Genetic
chemical_list: D004270:DNA, Circular; D012335:RNA, Ribosomal