Selection and characterization of nuclear mutations affecting mitochondria in Paramecium

A screening method, based upon resistance to a tetrazolium salt (TTC), is described which permitted the isolation in Paramecium of 28 mutants resistant to TTC. These mutants displayed various defects in mitochondrial functions (cytochromic content cyanide insensitive respiration). Some mutations seemed to affect directly the respiration chain while others seemed to cause indirect modifications, possibly altering mitochondrial protein synthesis. Genetic analysis of four mutants showed in all that the resistance to TTC was of nuclear origin.