The mitoribosomes of a chloramphenicol-resistant cytoplasmic mutant of Tetrahymnea pyriformis differ from those of the wild strain.

The spontaneous CAP-resistant mutant, STR1, has been isolated from the sensitive St-strain of Tetrahymena pyriformis (Curgy et al., Biologie Cellulaire 37, 51-60, 1980; Perasso et al., Biologie Cellulaire 37, 45-50, 1980). The goal of the present work is to disclose if the resistance character is due to a modification in the mitoribosomes and if the CAP-treatment induces changes in their abundance and in their physico-chemical properties.The results show that the resistance character of the mutant is due to a reduced affinity of its mitoribosomes for CAP. This difference can be explained by modifications of at least one protein which is probably coded for by the mitochondrial genome.The mitoribosomes from CAP-treated sensitive cells tend to dissociate into their subunits and the electrophoretic pattern of their proteins suggests that at least two mitoribosomal proteins are necessary to bound the two subunits together. These proteins are probably translated in mitochondria.Finally, the CAP-treatment induces a decrease of the abundance of mitoribosomes in the sensitive cells whereas it induced an increase in the resistant cells. The latter change can be regarded as a regulatory mechanism owing to which a loss of efficiency of the mitoribosomes is compensated by their enlarged abundance.