Molecular complexity of Paramecium symbiont lambda deoxyribonucleic acid: Evidence for the presence of a multicopy genome

The Size and Structure of the DNA Genome of Symbiont Xenosome Particles in the Ciliate Parauronema acutum

“…Xenosomes were isolated and purified from xenosome-bearing protozoa by (1) a modification of a procedure previously described for the isolation of mu and pi symbionts of Paramecium (Soldo & Godoy, 1974), or (2) a procedure based on separation of the particles in discontinuous sucrose gradients. In the former method, instant sea water ( p = 1.015 g cmP3) (ISW), (Soldo & Merlin, 1972) was used instead of migration salt solution (Soldo & Godoy, 1974). The latter method, which has not been described previously, was as follows: Xenosome-bearing P. acutum from 1-41 of culture were collected in a de Lava1 continuous-flow centrifuge or by pelleting the animals at IOOOg for 5 min at 4 OC in 125 ml capacity conical centrifuge bottles.…”

“…DNA was extracted from freshly isolated xenosomes by the procedure of Marmur (1 961). DNA from freshly harvested xenosome-bearing and xenosome-free protozoa was extracted as described by Soldo & Godoy (1973). CsCl density gradient centrifugation was used for final purification of the DNA preparations.…”

“…Thermal transition was followed by heating native DNA in standard saline citrate (SSC, containing 0.15 mol NaCl and 0.015 mol trisodium citrate 1-I) at a rate of 0.5 "C min-' during melting in a stoppered quartz cuvette ( I cm light path) in a Gilford model 250 spectrophotometer using the automatic thermo-programmer. Denaturation and renaturation of the DNA samples were accomplished as previously described (Soldo & Godoy, 1973). The reaction was followed at 260 nm.…”

“…Alkaline sedimentation coefficients were estimated by the method of Studier (1965) using alkaline sucrose gradients calibrated by the procedures described by Martin & Ames (1961). The kinetic complexity of the DNA samples was calculated from the renaturation rate constant and alkaline sedimentation coefficient using the formula of Wetmur & Davidson (1968), as previously described (Soldo & Godoy, 1973).…”

Studies on Protein Synthesis in Kappa Particles

“…Adaptation to an intracellular mode of life has led to degenerative changes : most symbionts are slow growing, and have lost their capacity to grow outside their host. The genome size of several endosymbionts appears to be small (Soldo & Godoy, 1973Schmidt, 1982), and the genome seems to be present in a rather high number of copies (5-20) per cell. Numerous other studies have shown the closeness of the relationship between symbionts and host.…”