a) Structure of N. ovalis macronuclear chromosomes. 1a-0.4% Agarose gel: M1 = λ- DNA (48502 bp). M2 = λ Eco RI/HindIII (sizes of the DNA fragments: 21226, 5148+4973, 4268, 3530, 2027, 1904, 1584 and 1375 bp). Lane 1,2 and 3 contain total DNA of Nyctotherus ovalis. Lane 4 contains total DNA of Euplotes crassus. Arrows indicate the ribosomal clusters (see Materials). b) Length distribution of the sequenced full-length macronuclear chromosomes. c) Southern blotting: unrestricted total DNA of N. ovalis was separated on a 0.7% agarose gel, blotted and hybridized with clones containing the α2 tubulin (α tub) and the β2 tubulin gene of Stylonychia lemnae. The labeling of single, gene-sized bands indicates the presence of tubulin genes on gene-sized DNA molecules.