Journal of Cell Science, Vol 11, 611-619, Copyright © 1972 by Company of Biologists

Submitted on December 23, 1971

The Basis of Cell-to-cell Transformation in Paramecium Bursaria

II. Investigation Into The Molecular Nature Of The Transforming Agent

¹ School of Biological Sciences, University of East Anglia, Norwich, England; John Innes Institute, Colney Lane, Norwich, England

A mating type transformation occurring in syngen 4 of Paramecium bursaria has been further investigated. The transformation event was not reversed or prevented by acridine or ionizing radiations. The transformation has not been accomplished with cell-free extracts including the microinjection of cytoplasmic extracts.

The nucleic acids of normal and transformed cells have been compared. No differences were found. Both types had 2 major ribosomal RNAs of molecular weights 1.29x10⁶ and 0.70x10⁶ Daltons. In both types a particular RNA species, with molecular weight 1.0x10⁵ Daltons, was found only in sexually competent cells. The DNA had a buoyant density in caesium chloride of 1.689 g cm^-3 and a T_m in 0.1xSSC (1xSSC=0.15 M sodium chloride, 0.015 M trisodium citrate) of 65.2°C. The renaturation kinetics showed 2 types of DNA - a fast-renaturing component, comprising 13% of the total DNA, with a complexity of 1.84x10⁹ Daltons, and a slow-renaturing component with a complexity of 1.6x10¹¹ Daltons, in both normal and transformed cells. Possible models for the action of the transforming agent are discussed.